Summary of Significant Accounting Policies (Adoption of New Accounting Pronouncements) (Details) - USD ($) $ / shares in Units, $ 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	Jan. 01, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Effective income tax rate reconciliation, share-based compensation, excess tax benefit, amount									$ 10
Net income	$ 897	$ 199	$ 141	$ 109	$ 153	$ 187	$ 134	$ 92	$ 1,346	$ 566	$ 585
Diluted earnings per share (in dollars per share)	$ 10.45	$ 2.33	$ 1.65	$ 1.27	$ 1.80	$ 2.16	$ 1.52	$ 1.01	$ 15.73	$ 6.45	$ 6.07
Excess tax benefits from share-based payment arrangements									$ 0	$ 58	$ 5
Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income									$ 10
Diluted earnings per share (in dollars per share)									$ 0.11
Owned Equipment Rentals | Product concentration risk | Equipment rental revenue
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of equipment rental revenue									86.00%
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income									$ 1,346	566	$ 585
Cumulative effect of a change in accounting for share-based payments					$ 5					$ 5
Retained Earnings | Accounting Standards Update 2016-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of a change in accounting for share-based payments												$ 5