Acquisitions (Purchase Price Allocation - NES Acquisition) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Apr. 30, 2017	Dec. 31, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 5,058	$ 4,082		$ 3,260	$ 3,243
NES
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