Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 5,765	$ 5,956
Credit risk derivatives, at fair value, net	(161)	(185)
Expected loss to be recovered	14	4
Public Finance [Member] | Non United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,327	2,676
Credit risk derivatives, at fair value, net	(29)	(39)
Public Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,195	1,942
Credit risk derivatives, at fair value, net	(66)	(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	(5)	(5)
Structured Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,119	1,206
Credit risk derivatives, at fair value, net	$ (61)	$ (58)