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Segment Information (Reconciliation to consolidated totals) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit	$ 998	$ 938	$ 782	$ 646	$ 827	$ 773	$ 655	$ 514	$ 3,364	$ 2,769	$ 2,403
Selling, general and administrative expenses									(1,038)	(903)	(719)
Merger related costs	(22)				(18)				(36)	(50)	0
Restructuring charge	$ (16)				$ (22)				(31)	(50)	(14)
Non-rental depreciation and amortization									(308)	(259)	(255)
Interest expense, net									(481)	(464)	(511)
Other income, net									6	5	5
Income before provision (benefit) for income taxes									1,476	1,048	909
Equipment rentals
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									2,963	2,440	2,089
Other products and services
Segment Reporting, Reconciling Item for Operating Profit (Loss) from Segment to Consolidated [Line Items]
Gross profit									$ 401	$ 329	$ 314