Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Mar. 31, 2021	Dec. 31, 2020
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 5,164	$ 5,371
Net Fair Value Asset (Liability)	(120)	(100)
Expected loss to be recovered	(2)	1
Public finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,817	1,980
Net Fair Value Asset (Liability)	(44)	(38)
Public finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	2,264	2,257
Net Fair Value Asset (Liability)	(32)	(27)
Structured finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	945	997
Net Fair Value Asset (Liability)	(40)	(30)
Structured finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	138	137
Net Fair Value Asset (Liability)	$ (4)	$ (5)