Contracts Accounted for as Credit Derivatives - Net Change in Fair Value of Credit Derivatives Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Credit Derivatives
Realized gains on credit derivatives	$ 3	$ 2
Net credit derivative losses (paid and payable) recovered and recoverable and other settlements	(4)	0
Realized gains (losses) and other settlements	(1)	2
Net unrealized gains (losses):
Net change in unrealized gains (losses) on credit derivatives	(21)	32
Net change in fair value of credit derivatives	$ (22)	$ 34