Revenue Revenue - Remaining Performance Obligation (Details) - Operating Segments - Automotive - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 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	$ (350)	$ (220)
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	285	269	$ 590	$ 567
Capitalized Contract Cost, Net	258		258		$ 247
Capitalized Contract Cost, Amortization	$ 20	$ 19	$ 39	$ 37
Other revenue | Minimum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	1 year		1 year
Other revenue | Maximum
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Period	2 years		2 years