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, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Realized gains on credit derivatives	$ 2	$ 2	$ 6	$ 6
Net credit derivative losses (paid and payable) recovered and recoverable and other settlements	(5)	(1)	(30)	(2)
Realized gains (losses) and other settlements	(3)	1	(24)	4
Net change in unrealized gains (losses) on credit derivatives	8	20	(1)	99
Net change in fair value of credit derivatives	$ 5	$ 21	$ (25)	$ 103