Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty revenue	$ 3,779	$ 3,402	$ 2,941
Contract with customer, liability, revenue recognized	971	834
Deferred non-insurance warranty acquisition expense	2,840	2,513	$ 2,094
Amortization of deferred sales commissions	813	673
Capitalized Commission Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	2,800	2,500
Capitalized Administrator Service Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 31	$ 24