Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty revenue	$ 4,023	$ 3,779
Contract with customer, liability, revenue recognized	1,100	971
Deferred non-insurance warranty acquisition expense	3,068	2,840
Amortization of deferred sales commissions	897	813
Capitalized Commission Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	3,100	2,800
Capitalized Administrator Service Costs
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred non-insurance warranty acquisition expense	$ 37	$ 31