Expected Loss to be Paid (Recovered) - Narrative (Details) $ in Millions		3 Months Ended	12 Months Ended
	Jun. 30, 2022	Sep. 30, 2022	Dec. 31, 2022 USD ($) Payment Curve scenario	Dec. 31, 2021 USD ($) scenario	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Expected Losses to be Paid [Line Items]
Period of insured credit performance of guaranteed obligations (in some cases over)			30 years
Net Par Outstanding			$ 233,258	$ 236,392
Net Expected Loss to be Paid (Recovered)			522	411	$ 529	$ 737
Economic benefit for public finance transactions			$ 125	$ 287	(145)
Projected loss assumptions, number of scenarios considered | scenario			5	5
Recovery period			5 years
Additional increase in recovery projection, percent			40.00%
Additional increase in recovery projection, economic benefit			$ 37
Additional decrease in recovery projection, percent			20.00%
Additional decrease in recovery projection, economic loss			$ 37
Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			224,099	$ 227,164
Net Expected Loss to be Paid (Recovered)			412	209	341	554
Economic benefit for public finance transactions			(17)	204	(203)
Other structured finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			7,203	6,837
Net Expected Loss to be Paid (Recovered)			44	52	40	37
Economic benefit for public finance transactions			(1)	(17)	(13)
BIG
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			5,892	7,356
BIG | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			4,777	5,972
BIG | Other structured finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			105	119
BIG | Student Loan
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			47
BIG | Life insurance transactions
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			40
U.S.
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			187,864
U.S. | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			179,636	177,219
Net Expected Loss to be Paid (Recovered)			403	197	305	531
Economic benefit for public finance transactions			(19)	182	(190)
U.S. | RMBS
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			1,956	2,391
Net Expected Loss to be Paid (Recovered)			66	150	148	146
Economic benefit for public finance transactions			$ 143	100	71
Maximum number of payments behind to be considered performing borrower | Payment			2
Period of maximum missed payments to be classified as performing borrower			2 years
U.S. | RMBS | Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Period to reach intermediate conditional default rate			12 months
U.S. | RMBS | First Lien
Schedule of Expected Losses to be Paid [Line Items]
Economic benefit for public finance transactions			$ (36)	0	45
Number of delinquent payments | Payment			2
Projected loss assumptions, CDR, plateau rate, projection period			36 months
Final conditional prepayment rates, term			12 months
Deferred loan balances to be recovered, percent			20.00%
Intermediate conditional default rate (as a percent)			5.00%
U.S. | RMBS | First Lien | Base Scenario
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period			36 months
Period to reach intermediate conditional default rate			12 months
Final conditional default rate as a percentage of plateau conditional default rate			5.00%
Projected loss assumptions, Final CDR, Period for voluntary prepayments to continue			1 year
Period for which estimated defaults are attributed to loans currently delinquent or in foreclosure			36 months
Projected loss assumptions, loss severity, subsequent period			18 months
Estimated loss severity rate, one through six months (as a percent)			18 months
Loss severity (as a percent)			40.00%
Projected loss assumptions, period to reach final loss severity rate			2 years 6 months
U.S. | RMBS | First Lien | More Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Period to reach intermediate conditional default rate			16 months
Projected loss assumptions, period to reach final loss severity rate			9 years
Projected loss assumptions, increase (decrease) in expected loss to be paid, net			$ 13
U.S. | RMBS | First Lien | Least Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period			30 months
Period to reach intermediate conditional default rate			8 months
Projected loss assumptions, increase (decrease) in expected loss to be paid, net			$ 8
Decrease in the plateau period used to calculate potential change in loss estimate (in months)			6 months
U.S. | RMBS | Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Economic benefit for public finance transactions			$ 107	$ 100	26
Liquidation rate			30.00%
Period to reach intermediate conditional default rate	28 months
Period of consistent CDR	6 months	36 months
Stress period (in months)	34 months	48 months
Period of delinquency (in days)			180 days
Percentage of consistent conditional default rate		5.00%
Conditional prepayment rate, final rate			15.00%
Loss recovery assumption			2.00%	2.00%
Number of conditional default rate curves modeled in estimating losses | Curve			5
U.S. | RMBS | Second Lien | Base Scenario
Schedule of Expected Losses to be Paid [Line Items]
Period to reach intermediate conditional default rate			28 months
Current conditional prepayment rate used in alternate scenario for loss estimate (as a percent)			15.00%
Stress period (in months)			34 months
Period of constant conditional default rate (in months)			6 months
U.S. | RMBS | Second Lien | More Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period			42 months
Period to reach intermediate conditional default rate			16 months
Stress period (in months)			58 months
Increase in conditional default rate ramp down period			4 months
U.S. | RMBS | Second Lien | More Stressful Environment | Home Equity Line of Credit
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for increased conditional default rate plateau period			$ 1
U.S. | RMBS | Second Lien | Least Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Stress period (in months)			38 months
Period of constant conditional default rate (in months)			30 months
Decreased conditional default rate ramp down period			8 months
Ultimate prepayment rate			10.00%
U.S. | RMBS | Second Lien | Least Stressful Environment | Home Equity Line of Credit
Schedule of Expected Losses to be Paid [Line Items]
Change in estimate for decreased conditional default rate ramp down period			$ 2
U.S. | RMBS | Second Lien | Base Scenario One
Schedule of Expected Losses to be Paid [Line Items]
Projected loss assumptions, CDR, plateau rate, projection period			36 months
Stress period (in months)			48 months
U.S. | Home Equity Line of Credit
Schedule of Expected Losses to be Paid [Line Items]
Initial period for which borrower can pay only interest payments			10 years
Modified loans reset to fully amortize, percent			80.00%
U.S. | Home Equity Line of Credit Insured
Schedule of Expected Losses to be Paid [Line Items]
Initial period for which borrower can pay only interest payments			15 years
U.S. | BIG | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			$ 3,796	$ 5,372
U.S. | BIG | RMBS
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			1,010	1,265
Non U.S.
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			45,394
Non U.S. | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			44,463	49,945
Net Expected Loss to be Paid (Recovered)			9	12	36	$ 23
Economic benefit for public finance transactions			2	22	$ (13)
Non U.S. | BIG | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Par Outstanding			$ 981	$ 600