Derivatives (Effect of derivatives on consolidated statements of income) (Details) gal in Millions, $ in Millions		12 Months Ended
	Dec. 31, 2017 gal	Dec. 31, 2017 USD ($) gal	Dec. 31, 2016 USD ($) gal	Dec. 31, 2015 USD ($) gal
Diesel swap | Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, amount of hedged item, volume, used (in gallons) | gal		6.7	10.1	10.6
Diesel swap | Designated as hedging instrument | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative (less than 1 for fixed price diesel swaps located in other income (expense), net, and cost of equipment rental for 2017)		$ 0	$ 0	$ 0
Diesel swap | Designated as hedging instrument | Cost of equipment rentals, excluding depreciation
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative (less than 1 for fixed price diesel swaps located in other income (expense), net, and cost of equipment rental for 2017)		0	(6)	(7)
Amount of income (expense) recognized on hedged item		(18)	(23)	(29)
Forward contracts | Not designated as hedging instrument | Other income (expense), net
Derivative Instruments, Gain (Loss) [Line Items]
Amount of income (expense) recognized on derivative (less than 1 for fixed price diesel swaps located in other income (expense), net, and cost of equipment rental for 2017)		13	(3)	(5)
Amount of income (expense) recognized on hedged item		$ (13)	$ 3	$ 5
Cash Flow Hedging | Diesel swap | Designated as hedging instrument
Derivative Instruments, Gain (Loss) [Line Items]
Derivative, nonmonetary notional amount (in gallons) | gal	4.7