Leases (Capital Lease Obligations) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Operating Leased Assets [Line Items]
Less accumulated depreciation and amortization	$ (12)
Rental equipment, net	10
Capital lease obligations	122
Rent expense on non-cancelable leases	179	$ 160
Rental equipment, net
Operating Leased Assets [Line Items]
Depreciation and amortization	22	21
Capital leased assets	257
Less accumulated depreciation and amortization	(86)
Rental equipment, net	171
Rent expense on short term non-cancelable leases	121	94
Non-rental depreciation and amortization
Operating Leased Assets [Line Items]
Depreciation and amortization	1	$ 2
Non-rental vehicles
Operating Leased Assets [Line Items]
Capital leased assets	6
Building
Operating Leased Assets [Line Items]
Capital leased assets	$ 16