Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 6,165	$ 6,182
Credit risk derivatives, at fair value, net	(208)	(207)
Expected loss to be recovered	5	2
Public Finance [Member] | Non United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,709	2,807
Credit risk derivatives, at fair value, net	(46)	(51)
Public Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,067	1,783
Credit risk derivatives, at fair value, net	(103)	(65)
Structured Finance [Member] | Non United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	123	127
Credit risk derivatives, at fair value, net	(8)	(6)
Structured Finance [Member] | United States [Member]
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,266	1,465
Credit risk derivatives, at fair value, net	$ (51)	$ (85)