SEGMENT INFORMATION - Segment Information by Segment (Detail) - USD ($)
$ in Millions
 3 Months Ended 9 Months Ended
Sep. 30, 2016
Sep. 30, 2015
Sep. 30, 2016
Sep. 30, 2015
Segment Reporting Information [Line Items]        
Premiums $ 13,371 $ 12,987 $ 40,461 $ 39,447
Services 227 246 749 1,143
Total revenues - external customers 13,598 13,233 41,210 40,590
Investment income 96 130 291 338
Total revenues 13,694 13,363 41,501 40,928
Benefits 10,900 10,896 33,806 33,153
Operating costs 1,759 1,688 5,253 5,450
Depreciation and amortization 86 84 263 267
Total operating expenses 12,745 12,668 39,322 38,870
Income from operations 949 695 2,179 2,058
Gain on sale of business 0 0 0 267
Interest expense 47 47 141 140
Income before income taxes 902 648 2,038 2,185
Individual Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 7,977 7,316 24,054 22,183
Group Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 1,067 1,396 3,229 4,188
Medicare stand-alone PDP        
Segment Reporting Information [Line Items]        
Premiums 1,004 927 3,058 2,915
Total Medicare        
Segment Reporting Information [Line Items]        
Premiums 10,048 9,639 30,341 29,286
Fully-insured        
Segment Reporting Information [Line Items]        
Premiums 2,341 2,418 7,162 7,388
Specialty        
Segment Reporting Information [Line Items]        
Premiums 318 326 957 990
Medicaid and other        
Segment Reporting Information [Line Items]        
Premiums 664 604 2,001 1,783
Provider        
Segment Reporting Information [Line Items]        
Services 69 70 214 619
ASO and other        
Segment Reporting Information [Line Items]        
Services 150 168 513 502
Pharmacy        
Segment Reporting Information [Line Items]        
Services 8 8 22 22
Intersegment revenues        
Segment Reporting Information [Line Items]        
Total revenues (6,311) (5,853) (18,638) (17,079)
Intersegment revenues | Retail        
Segment Reporting Information [Line Items]        
Total revenues 0 0 0 0
Intersegment revenues | Group        
Segment Reporting Information [Line Items]        
Total revenues 23 24 67 68
Intersegment revenues | Healthcare Services        
Segment Reporting Information [Line Items]        
Total revenues 6,288 5,829 18,571 17,011
Intersegment revenues | Services        
Segment Reporting Information [Line Items]        
Total revenues (4,731) (4,582) (14,265) (13,425)
Intersegment revenues | Services | Retail        
Segment Reporting Information [Line Items]        
Total revenues 0 0 0 0
Intersegment revenues | Services | Group        
Segment Reporting Information [Line Items]        
Total revenues 23 24 67 68
Intersegment revenues | Services | Healthcare Services        
Segment Reporting Information [Line Items]        
Total revenues 4,708 4,558 14,198 13,357
Intersegment revenues | Products        
Segment Reporting Information [Line Items]        
Total revenues (1,580) (1,271) (4,373) (3,654)
Intersegment revenues | Products | Retail        
Segment Reporting Information [Line Items]        
Total revenues 0 0 0 0
Intersegment revenues | Products | Group        
Segment Reporting Information [Line Items]        
Total revenues 0 0 0 0
Intersegment revenues | Products | Healthcare Services        
Segment Reporting Information [Line Items]        
Total revenues 1,580 1,271 4,373 3,654
Operating Segments | Retail        
Segment Reporting Information [Line Items]        
Premiums 11,756 11,353 35,615 34,486
Services 3 1 7 7
Total revenues - external customers 11,759 11,354 35,622 34,493
Investment income 25 38 77 96
Total revenues 11,784 11,392 35,699 34,589
Benefits 9,771 9,777 30,581 29,781
Operating costs 1,308 1,241 3,825 3,708
Depreciation and amortization 61 49 175 140
Total operating expenses 11,140 11,067 34,581 33,629
Income from operations 644 325 1,118 960
Gain on sale of business       0
Interest expense 0 0 0 0
Income before income taxes 644 325 1,118 960
Operating Segments | Group        
Segment Reporting Information [Line Items]        
Premiums 1,605 1,628 4,817 4,936
Services 158 171 537 514
Total revenues - external customers 1,763 1,799 5,354 5,450
Investment income 4 7 13 18
Total revenues 1,790 1,830 5,434 5,536
Benefits 1,327 1,341 3,794 3,908
Operating costs 430 426 1,300 1,323
Depreciation and amortization 21 24 69 69
Total operating expenses 1,778 1,791 5,163 5,300
Income from operations 12 39 271 236
Gain on sale of business       0
Interest expense 0 0 0 0
Income before income taxes 12 39 271 236
Operating Segments | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Services 65 69 198 612
Total revenues - external customers 65 69 198 612
Investment income 8 0 22 0
Total revenues 6,361 5,898 18,791 17,623
Benefits 0 0 0 0
Operating costs 6,040 5,584 17,894 16,774
Depreciation and amortization 33 30 97 112
Total operating expenses 6,073 5,614 17,991 16,886
Income from operations 288 284 800 737
Gain on sale of business       0
Interest expense 0 0 0 0
Income before income taxes 288 284 800 737
Operating Segments | Individual Medicare Advantage | Retail        
Segment Reporting Information [Line Items]        
Premiums 7,977 7,316 24,054 22,183
Operating Segments | Individual Medicare Advantage | Group        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Individual Medicare Advantage | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Group Medicare Advantage | Retail        
Segment Reporting Information [Line Items]        
Premiums 1,067 1,396 3,229 4,188
Operating Segments | Group Medicare Advantage | Group        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Group Medicare Advantage | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Medicare stand-alone PDP | Retail        
Segment Reporting Information [Line Items]        
Premiums 1,004 927 3,058 2,915
Operating Segments | Medicare stand-alone PDP | Group        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Medicare stand-alone PDP | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Total Medicare | Retail        
Segment Reporting Information [Line Items]        
Premiums 10,048 9,639 30,341 29,286
Operating Segments | Total Medicare | Group        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Total Medicare | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Fully-insured | Retail        
Segment Reporting Information [Line Items]        
Premiums 991 1,056 3,118 3,263
Operating Segments | Fully-insured | Group        
Segment Reporting Information [Line Items]        
Premiums 1,350 1,362 4,044 4,125
Operating Segments | Fully-insured | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Specialty | Retail        
Segment Reporting Information [Line Items]        
Premiums 65 66 196 195
Operating Segments | Specialty | Group        
Segment Reporting Information [Line Items]        
Premiums 253 260 761 795
Operating Segments | Specialty | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Medicaid and other | Retail        
Segment Reporting Information [Line Items]        
Premiums 652 592 1,960 1,742
Operating Segments | Medicaid and other | Group        
Segment Reporting Information [Line Items]        
Premiums 2 6 12 16
Operating Segments | Medicaid and other | Healthcare Services        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Operating Segments | Provider | Retail        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Operating Segments | Provider | Group        
Segment Reporting Information [Line Items]        
Services 12 9 38 29
Operating Segments | Provider | Healthcare Services        
Segment Reporting Information [Line Items]        
Services 57 61 176 590
Operating Segments | ASO and other | Retail        
Segment Reporting Information [Line Items]        
Services 3 1 7 7
Operating Segments | ASO and other | Group        
Segment Reporting Information [Line Items]        
Services 146 162 499 485
Operating Segments | ASO and other | Healthcare Services        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Operating Segments | Pharmacy | Retail        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Operating Segments | Pharmacy | Group        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Operating Segments | Pharmacy | Healthcare Services        
Segment Reporting Information [Line Items]        
Services 8 8 22 22
Other Businesses        
Segment Reporting Information [Line Items]        
Premiums 10 6 29 25
Services 1 5 7 10
Total revenues - external customers 11 11 36 35
Investment income 17 16 48 53
Total revenues 28 27 84 88
Benefits 26 22 82 66
Operating costs 4 3 12 10
Depreciation and amortization 0 0 0 0
Total operating expenses 30 25 94 76
Income from operations (2) 2 (10) 12
Gain on sale of business       0
Interest expense 0 0 0 0
Income before income taxes (2) 2 (10) 12
Other Businesses | Individual Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Group Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Medicare stand-alone PDP        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Total Medicare        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Fully-insured        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Specialty        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Other Businesses | Medicaid and other        
Segment Reporting Information [Line Items]        
Premiums 10 6 29 25
Other Businesses | Provider        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Other Businesses | ASO and other        
Segment Reporting Information [Line Items]        
Services 1 5 7 10
Other Businesses | Pharmacy        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Eliminations/ Corporate        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Services 0 0 0 0
Total revenues - external customers 0 0 0 0
Investment income 42 69 131 171
Total revenues (6,269) (5,784) (18,507) (16,908)
Benefits (224) (244) (651) (602)
Operating costs (6,023) (5,566) (17,778) (16,365)
Depreciation and amortization (29) (19) (78) (54)
Total operating expenses (6,276) (5,829) (18,507) (17,021)
Income from operations 7 45 0 113
Gain on sale of business       267
Interest expense 47 47 141 140
Income before income taxes (40) (2) (141) 240
Eliminations/ Corporate | Individual Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Group Medicare Advantage        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Medicare stand-alone PDP        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Total Medicare        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Fully-insured        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Specialty        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Medicaid and other        
Segment Reporting Information [Line Items]        
Premiums 0 0 0 0
Eliminations/ Corporate | Provider        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Eliminations/ Corporate | ASO and other        
Segment Reporting Information [Line Items]        
Services 0 0 0 0
Eliminations/ Corporate | Pharmacy        
Segment Reporting Information [Line Items]        
Services $ 0 $ 0 $ 0 $ 0