Acquisitions (Purchase Price Allocation - NES Acquisition) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Apr. 30, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$ 4,082		$ 3,260	$ 3,243	$ 3,272
NES Rentals Holdings II, Inc.
Business Acquisition [Line Items]
Accounts receivable, net of allowance for doubtful accounts		$ 49
Inventory		4
Rental equipment		571
Property and equipment		48
Intangibles		139
Other assets		7
Total identifiable assets acquired		818
Short-term debt and current maturities of long-term debt		(3)
Current liabilities		(33)
Deferred taxes		(15)
Long-term debt		(11)
Other long-term liabilities		(5)
Total liabilities assumed		(67)
Net identifiable assets acquired		751
Goodwill		209
Net assets acquired		960
Accounts receivable, gross		53
Accounts receivable, allowance for doubtful accounts		4
Goodwill expected to be deductible for tax purposes		$ 1