Contracts Accounted for as Credit Derivatives - Net Change in Fair Value of Credit Derivatives Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Realized gains on credit derivatives	$ 1	$ 2	$ 4	$ 6
Net credit derivative losses (paid and payable) recovered and recoverable and other settlements	(6)	(5)	(9)	(30)
Realized gains (losses) and other settlements	(5)	(3)	(5)	(24)
Net unrealized gains (losses)	2	8	25	(1)
Net change in fair value of credit derivatives	$ (3)	$ 5	$ 20	$ (25)