Non-Insurance Revenues from Contracts with Customers (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue from Contract with Customer [Abstract]
Deferred non-insurance warranty revenue	$ 4,443		$ 4,443		$ 4,023
Contract with customer, liability, revenue recognized	$ 300	$ 300	$ 900	$ 800