Segment Information (Financial information by segment) (Details) (USD $)
In Millions, unless otherwise specified
 3 Months Ended 12 Months Ended
Dec. 31, 2014
Sep. 30, 2014
Jun. 30, 2014
Mar. 31, 2014
Dec. 31, 2013
Sep. 30, 2013
Jun. 30, 2013
Mar. 31, 2013
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Segment Reporting Information [Line Items]                      
Equipment rentals                 $ 4,819 $ 4,196 $ 3,455
Sales of rental equipment                 544 490 399
Sales of new equipment                 149 104 93
Contractor supplies sales                 85 87 87
Service and other revenues                 88 78 83
Total revenues 1,564 [1] 1,544 [1] 1,399 [1] 1,178 [1] 1,338 [2] 1,311 [2] 1,206 [2] 1,100 [2] 5,685 [1] 4,955 [2] 4,117
Depreciation and amortization expense                 1,194 1,098 897
Gross profit 707 [1] 688 [1] 589 [1] 448 [1] 567 [2] 564 [2] 471 [2] 385 [2] 2,432 [1] 1,987 [2] 1,587
Capital expenditures                 1,821 1,684 1,369
Total assets (1) 12,467 [3]       11,231 [3]       12,467 [3] 11,231 [3]  
Operating segments | General rentals                      
Segment Reporting Information [Line Items]                      
Equipment rentals                 4,222 3,869 3,188
Sales of rental equipment                 519 474 387
Sales of new equipment                 113 97 86
Contractor supplies sales                 73 79 80
Service and other revenues                 75 72 79
Total revenues                 5,002 4,591 3,820
Depreciation and amortization expense                 1,060 1,038 850
Capital expenditures                 1,594 1,556 1,285
Total assets (1) 10,935 [3]       10,677 [3]       10,935 [3] 10,677 [3]  
Operating segments | Trench safety, Power and HVAC, and Pump Solutions                      
Segment Reporting Information [Line Items]                      
Equipment rentals                 597 327 267
Sales of rental equipment                 25 16 12
Sales of new equipment                 36 7 7
Contractor supplies sales                 12 8 7
Service and other revenues                 13 6 4
Total revenues                 683 364 297
Depreciation and amortization expense                 134 60 47
Capital expenditures                 227 128 84
Total assets (1) 1,532 [3]       554 [3]       1,532 [3] 554 [3]  
Equipment rentals                      
Segment Reporting Information [Line Items]                      
Gross profit                 2,092 1,710 1,364
Equipment rentals | Operating segments | General rentals                      
Segment Reporting Information [Line Items]                      
Gross profit                 1,790 1,557 1,239
Equipment rentals | Operating segments | Trench safety, Power and HVAC, and Pump Solutions                      
Segment Reporting Information [Line Items]                      
Gross profit                 $ 302 $ 153 $ 125
[1] The fourth quarter of 2014 includes an increase in bad debt expense of $8 as compared to the fourth quarter of 2013 primarily due to improved receivable aging which reduced the expense in the fourth quarter of 2013. Additionally, the fourth quarter of 2014 includes an increase in stock compensation, net of $14 as compared to the fourth quarter of 2013 primarily due to improved profitability which resulted in increased performance based stock compensation.
[2] The fourth quarter of 2013 includes a reduction in bad debt expense of $17 as compared to the fourth quarter of 2012 primarily due to improved receivable aging. In the fourth quarter of 2013, we recognized a benefit of $3 in cost of equipment rentals, excluding depreciation related to our provision for self-insurance reserves.
[3] The increase in the trench safety, power and HVAC, and pump solutions assets in 2014 primarily reflects the impact of the National Pump acquisition discussed in note 3 to the consolidated financial statements.