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.