Derivatives (Effect of derivatives on consolidated statements of income) (Details) gal in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017 USD ($) gal	Sep. 30, 2016 USD ($) gal	Sep. 30, 2017 USD ($) gal	Sep. 30, 2016 USD ($) gal
Fixed price diesel swaps | Derivatives designated as hedging instruments:
Derivative Instruments, Gain (Loss) [Line Items]
Purchases of diesel covered by the fixed price swaps (in gallons) | gal	1.7	2.7	5.5	7.7
Fixed price diesel swaps | Derivatives designated as hedging instruments: | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative	$ 0	$ 0	$ 0	$ 0
Fixed price diesel swaps | Derivatives designated as hedging instruments: | Cost of equipment rentals, excluding depreciation
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative	0	(1)	0	(5)
Amount of income (expense) recognized on hedged item	(4)	(6)	(14)	(17)
Foreign currency forward contracts | Derivatives not designated as hedging instruments: | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative	8	(4)	15	(1)
Amount of income (expense) recognized on hedged item	$ (8)	$ 4	$ (15)	$ 1