Segment Information (Reconciliation to consolidated totals) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit	$ 827	$ 773	$ 655	$ 514	$ 657	$ 656	$ 590	$ 500	$ 2,769	$ 2,403	$ 2,480
Selling, general and administrative expenses									(903)	(719)	(714)
Merger related costs	(18)								(50)	0	26
Restructuring charge	$ (22)								(50)	(14)	(6)
Non-rental depreciation and amortization									(259)	(255)	(268)
Interest expense, net									(464)	(511)	(567)
Other income, net									5	5	12
Income before (benefit) provision for income taxes									1,048	909	963
Equipment Rentals, Operating Lease
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									2,440	2,089	2,147
Other products and services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									$ 329	$ 314	$ 333