Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 5,806	$ 5,956
Credit risk derivatives, at fair value, net	(262)	(185)
Expected loss to be recovered	13	4
Public Finance [Member] | Non United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,461	2,676
Credit risk derivatives, at fair value, net	(52)	(39)
Public Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,065	1,942
Credit risk derivatives, at fair value, net	(112)	(83)
Structured Finance [Member] | Non United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	124	132
Credit risk derivatives, at fair value, net	(9)	(5)
Structured Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,156	1,206
Credit risk derivatives, at fair value, net	$ (89)	$ (58)