Contracts Accounted for as Credit Derivatives - Credit Derivatives Subordination and Ratings (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2024	Dec. 31, 2023
Credit Derivatives
Estimated remaining weighted average life of credit derivatives (in years)	10 years 10 months 24 days	11 years 1 month 6 days
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	$ 3,421	$ 3,608
Net Fair Value Asset (Liability)	(39)	(50)
Expected loss to be recovered	1	2
Public finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,077	1,149
Net Fair Value Asset (Liability)	(14)	(15)
Public finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	1,507	1,522
Net Fair Value Asset (Liability)	(19)	(20)
Structured finance | United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	223	322
Net Fair Value Asset (Liability)	(5)	(13)
Structured finance | Non United States
Net Par Outstanding on Credit Derivatives
Net Par Outstanding	614	615
Net Fair Value Asset (Liability)	$ (1)	$ (2)