Revenue Revenue - Remaining Performance Obligation (Details) - Operating Segments [Member] - Automotive - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017	Jan. 01, 2017
Vehicles, parts, and accessories
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue Performance Obligation Satisfied In Prior Period	$ (240)	$ (182)
Vehicles, parts, and accessories | Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue Performance Obligation Payment Terms			30 days
Vehicles, parts, and accessories | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue Performance Obligation Payment Terms			120 days
Extended service contracts
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with Customer, Liability					$ 3,800	$ 3,500
Contract with Customer, Liability, Revenue Recognized	262	256	$ 829	$ 797
Deferrred cost	242		242		$ 232
Amortization	$ 18	$ 17	$ 55	$ 46
Extended service contracts | Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue remaining performance obligation expected timing of satisfaction period			12 months
Extended service contracts | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue remaining performance obligation expected timing of satisfaction period			120 months
Other revenue | Minimum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue remaining performance obligation expected timing of satisfaction period			1 year
Other revenue | Maximum [Member]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue remaining performance obligation expected timing of satisfaction period			2 years