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, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Credit Derivatives
Realized gains on credit derivatives	$ 1	$ 2	$ 4	$ 4
Net credit derivative losses (paid and payable) recovered and recoverable and other settlements	(21)	(1)	(25)	(1)
Realized gains (losses) and other settlements	(20)	1	(21)	3
Net unrealized gains (losses):
Net change in unrealized gains (losses) on credit derivatives	12	47	(9)	79
Net change in fair value of credit derivatives	$ (8)	$ 48	$ (30)	$ 82