Contracts Accounted for as Credit Derivatives - Net Change in Fair Value of Credit Derivatives Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Realized gains on credit derivatives	$ 1	$ 1	$ 3	$ 4
Net credit derivative losses (paid and payable) recovered and recoverable and other settlements	(1)	(21)	(3)	(25)
Realized gains (losses) and other settlements	0	(20)	0	(21)
Net change in unrealized gains (losses) on credit derivatives	100	12	23	(9)
Net change in fair value of credit derivatives	$ 100	$ (8)	$ 23	$ (30)