Expected Loss to be Paid (Recovered) - Additional Information (Details) $ in Millions	3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2023 USD ($)	Mar. 31, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($) Payment Curve scenario	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($) scenario	Mar. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Schedule of Expected Losses to be Paid [Line Items]
Period of insured credit performance of guaranteed obligations (in some cases over)				30 years
Discount factor (as a percent)				4.34%		4.08%
Net Expected Loss to be Paid (Recovered)	$ 560	$ 517	$ 442	$ 560	$ 442	$ 522	$ 432	$ 411
Loss and LAE Reserve paid	5		7	8	20
Expected LAE to be paid	11			11		11
Net economic loss development (benefit)	49		(32)	$ 60	(76)
Additional loss recovery assumption, recovery period				5 years
First Lien
Schedule of Expected Losses to be Paid [Line Items]
Effect of recovery		1
Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Effect of recovery		1
Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	443	393	217	$ 443	217	412	191	209
Net economic loss development (benefit)	54		6	59	(44)
Other structured finance
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	44	42	46	44	46	$ 44	46	52
Net economic loss development (benefit)	4		1	$ 5	0
United States
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for representations and warranties, percent				98.30%		98.50%
United States | Public finance
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	433	380	210	$ 433	210	$ 403	181	197
Net economic loss development (benefit)	57		8	58	(40)
United States | RMBS
Schedule of Expected Losses to be Paid [Line Items]
Net Expected Loss to be Paid (Recovered)	73	$ 82	179	73	179	$ 66	$ 195	$ 150
Net economic loss development (benefit)	(9)		(39)	(4)	(32)
United States | RMBS | First Lien
Schedule of Expected Losses to be Paid [Line Items]
Net economic loss development (benefit)	$ 0		(14)	$ 0	4
Number of delinquent payments | Payment				2
Projected loss assumptions, CDR, plateau rate, projection period				36 months
Projected loss assumptions, final CPR, period for voluntary prepayments to continue				12 months
Intermediate conditional default rate (as a percent)	5.00%			5.00%
Number of scenarios weighted in estimating expected losses | scenario				5		5
United States | RMBS | First Lien | Base Scenario
Schedule of Expected Losses to be Paid [Line Items]
Percent of deferred loan balances to be recovered				20.00%		20.00%
United States | RMBS | First Lien | More Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Percent of deferred loan balances to be recovered		10.00%
United States | RMBS | First Lien | Least Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Percent of deferred loan balances to be recovered		50.00%
United States | 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 from plateau to intermediate conditional default rate (in months)				12 months
Final conditional default rate as a percentage of plateau conditional default rate				5.00%
Projected loss assumptions, final CPR, period for voluntary prepayments to continue				1 year
Default from delinquentor rate, term				36 months
Performing or projected to reperform, projection period				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%			40.00%
Projected loss assumptions, period to reach final loss severity rate				2 years 6 months
Final CPR	15.00%			15.00%
United States | RMBS | First Lien | More Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Period from plateau to intermediate conditional default rate (in months)				16 months
Projected loss assumptions, period to reach final loss severity rate				9 years
Percent of deferred loan balances to be recovered				10.00%
Projected loss assumptions, increase (decrease) in expected loss to be paid, net				$ 22
United States | 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 from plateau to intermediate conditional default rate (in months)				8 months
Percent of deferred loan balances to be recovered				50.00%
Projected loss assumptions, increase (decrease) in expected loss to be paid, net				$ (31)
Decrease in the plateau period used to calculate potential change in loss estimate (in months)				6 months
United States | RMBS | Second Lien
Schedule of Expected Losses to be Paid [Line Items]
Net economic loss development (benefit)	$ (9)		$ (25)	$ (4)	$ (36)
Projected loss assumptions, period of consistent conditional default rate				36 months
Period of conditional default rate downward trend				1 year
Percent of original period of consistent conditional default rate				5.00%
Loss recovery assumption (as a percent)	2.00%			2.00%		2.00%
Number of conditional default rate curves modeled in estimating losses | Curve				5
Liquidation rate	30.00%			30.00%
United States | RMBS | Second Lien | More Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Percent of deferred loan balances to be recovered				10.00%
United States | RMBS | Second Lien | Least Stressful Environment
Schedule of Expected Losses to be Paid [Line Items]
Percent of deferred loan balances to be recovered				50.00%
United States | RMBS | Second Lien | Home Equity Line of Credit and Closed-end Mortgage
Schedule of Expected Losses to be Paid [Line Items]
Final CPR	15.00%			15.00%
United States | 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 from plateau to intermediate conditional default rate (in months)				16 months
Stress period (in months)				58 months
Increase in conditional default rate ramp down period				4 months
United States | 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				$ (62)
United States | 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
Change in estimate for decreased prepayment rate, Percent				10.00%
United States | 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				$ 63
United States | 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
United States | 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
Minimum
Schedule of Expected Losses to be Paid [Line Items]
Risk free discount rate				3.73%		3.82%
Maximum
Schedule of Expected Losses to be Paid [Line Items]
Risk free discount rate				5.37%		4.69%