Summary of Significant Accounting Policies (Cumulative Effect to the Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 2,840	$ 2,513	$ 2,094
Deferred non-insurance warranty revenue	3,779	3,402	2,941
Deferred income taxes	199	392	158
Retained earnings	$ 9,348	9,277	9,348
Balance as of December 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense		2,116		$ 212
Deferred non-insurance warranty revenue		2,997		972
Deferred income taxes		390		137
Retained earnings		9,283		$ 9,414
Adjustments Due to Adoption of Topic 606
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense		397	1,882
Deferred non-insurance warranty revenue		405	1,969
Deferred income taxes		2	21
Retained earnings		$ (6)	$ (66)