Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty revenue	$ 3,402	$ 2,941	$ 972
Contract with customer, liability, revenue recognized	834
Deferred non-insurance warranty acquisition expense	2,513	$ 2,094	$ 212
Amortization of deferred sales commissions	673
Capitalized Commission Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	2,500
Capitalized Administrator Service Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 24