Consolidated Statements Of Income (USD $)
In Millions, except Per Share data, unless otherwise specified
 3 Months Ended 9 Months Ended
Sep. 30, 2012
Sep. 30, 2011
Sep. 30, 2012
Sep. 30, 2011
Operating Revenue $ 1,507 $ 1,464 $ 4,583 $ 4,883
Operating Expenses        
Fuel for electric generation 190 199 446 504
Purchased and interchange power 386 365 1,037 968
Purchased power - related parties 23 23 65 64
Cost of gas sold 80 107 763 1,095
Maintenance and other operating expenses 295 301 872 868
Depreciation and amortization 138 120 440 404
General taxes 53 33 170 151
Gain on asset sales, net (1)   (1)  
Total operating expenses 1,164 1,148 3,792 4,054
Operating Income 343 316 791 829
Other Income (Expense)        
Interest income 1 4 3 8
Allowance for equity funds used during construction 2 1 6 4
Income (loss) from equity method investees 5 4 13 10
Other income 3 3 9 12
Other expense (11) (3) (16) (8)
Total other income (expense)   9 15 26
Interest Charges        
Interest on long-term debt 92 99 280 298
Other interest expense 5 6 16 18
Allowance for borrowed funds used during construction (1) (1) (3) (3)
Total interest charges 96 104 293 313
Income Before Income Taxes 247 221 513 542
Income Tax Expense 98 81 203 168
Income From Continuing Operations 149 140 310 374
Income From Discontinued Operations, Net of Tax     7 2
Net Income 149 140 317 376
Income Attributable to Noncontrolling Interests 1 1 2 2
Net Income (Loss) Attributable to Parent 148 139 315 374
Net Income Available to Common Stockholders 148 139 315 374
Net Income Attributable to Common Stockholders        
Amounts attributable to continuing operations 148 139 308 372
Amounts attributable to discontinued operations     7 2
Net Income Available to Common Stockholders 148 139 315 374
Income Attributable to Noncontrolling Interests        
Amounts attributable to continuing operations 1 1 2 2
Income attributable to noncontrolling interests 1 1 2 2
Basic Earnings Per Average Common Share        
Basic earnings from continuing operations $ 0.56 $ 0.55 $ 1.18 $ 1.48
Basic earnings from discontinued operations     $ 0.03 $ 0.01
Basic earnings attributable to common stock $ 0.56 $ 0.55 $ 1.21 $ 1.49
Diluted Earnings Per Average Common Share        
Diluted earnings from continuing operations $ 0.55 $ 0.53 $ 1.14 $ 1.42
Diluted earnings from discontinued operations     $ 0.03 $ 0.01
Diluted earnings attributable to common stock $ 0.55 $ 0.53 $ 1.17 $ 1.43
Dividends Declared Per Common Share $ 0.24 $ 0.21 $ 0.72 $ 0.63
Consumers Energy Company [Member]
        
Operating Revenue 1,448 1,397 4,405 4,688
Operating Expenses        
Fuel for electric generation 166 175 382 442
Purchased and interchange power 379 362 1,019 954
Purchased power - related parties 23 24 65 64
Cost of gas sold 74 88 734 1,038
Maintenance and other operating expenses 284 286 827 824
Depreciation and amortization 137 119 436 401
General taxes 51 38 165 153
Total operating expenses 1,114 1,092 3,628 3,876
Operating Income 334 305 777 812
Other Income (Expense)        
Interest income   2 2 6
Interest and dividend income - related parties 1 1 1 1
Allowance for equity funds used during construction 2 1 6 4
Other income 3 3 14 16
Other expense (11) (3) (16) (8)
Total other income (expense) (5) 4 7 19
Interest Charges        
Interest on long-term debt 56 62 175 188
Other interest expense 4 5 12 14
Allowance for borrowed funds used during construction (1) (1) (3) (3)
Total interest charges 59 66 184 199
Income Before Income Taxes 270 243 600 632
Income Tax Expense 107 88 239 232
Net Income 163 155 361 400
Preferred Stock Dividends 1 1 2 2
Net Income Available to Common Stockholders 162 154 359 398
Net Income Attributable to Common Stockholders        
Net Income Available to Common Stockholders $ 162 $ 154 $ 359 $ 398