Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 4,286	$ 5,371
Net Fair Value Asset (Liability)	(134)	(100)
Expected loss to be recovered	6	(1)
Public finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,766	1,980
Net Fair Value Asset (Liability)	(60)	(38)
Public finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,953	2,257
Net Fair Value Asset (Liability)	(40)	(27)
Structured finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	432	997
Net Fair Value Asset (Liability)	(32)	(30)
Structured finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	135	137
Net Fair Value Asset (Liability)	$ (2)	$ (5)