Revenue Revenue - Remaining Performance Obligation (Details) - Operating Segments [Member] - Automotive - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Vehicles, parts, and accessories
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue Performance Obligation Satisfied In Prior Period	$ (481)	$ (718)
Extended service contracts
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Contract with Customer, Liability			$ 4,000	$ 3,800
Contract with Customer, Liability, Revenue Recognized	305	298
Deferred cost	256		$ 247
Amortization	$ 19	$ 18
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