Expected Loss to be Paid (Recovered) - Net Expected Loss to be Paid After Net Expected Recoveries for Breaches of R&W Rollforward (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022	Dec. 31, 2022
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	$ 517	$ 432	$ 522	$ 411	$ 411
Accretion of discount	4	3	9	5
Changes in discount rates	(6)	(42)	4	(89)
Changes in timing and assumptions	51	7	47	8
Total economic loss development (benefit)	49	(32)	60	(76)
Net (paid) recovered losses	(6)	42	(22)	107
Net expected loss to be paid (recovered), end of period	560	442	$ 560	442	$ 522
Weighted average risk free discount rate			4.34%		4.08%
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)			45 days
Minimum
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Risk free discount rate			3.73%		3.82%
Maximum
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Risk free discount rate			5.37%		4.69%
United States
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid after recoveries for representations and warranties, percent			98.30%		98.50%
Public finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	393	191	$ 412	209	$ 209
Total economic loss development (benefit)	54	6	59	(44)
Net (paid) recovered losses	(4)	20	(28)	52
Net expected loss to be paid (recovered), end of period	443	217	443	217	412
Public finance | United States
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	380	181	403	197	197
Total economic loss development (benefit)	57	8	58	(40)
Net (paid) recovered losses	(4)	21	(28)	53
Net expected loss to be paid (recovered), end of period	433	210	433	210	403
Public finance | Non-U.S. public finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	13	10	9	12	12
Total economic loss development (benefit)	(3)	(2)	1	(4)
Net (paid) recovered losses	0	(1)	0	(1)
Net expected loss to be paid (recovered), end of period	10	7	10	7	9
RMBS | United States
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	82	195	66	150	150
Total economic loss development (benefit)	(9)	(39)	(4)	(32)
Net (paid) recovered losses	0	23	11	61
Net expected loss to be paid (recovered), end of period	73	179	73	179	66
Other structured finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	42	46	44	52	52
Total economic loss development (benefit)	4	1	5	0
Net (paid) recovered losses	(2)	(1)	(5)	(6)
Net expected loss to be paid (recovered), end of period	44	46	44	46	44
Structured finance
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Net expected loss to be paid (recovered), beginning of period	124	241	110	202	202
Total economic loss development (benefit)	(5)	(38)	1	(32)
Net (paid) recovered losses	(2)	22	6	55
Net expected loss to be paid (recovered), end of period	$ 117	$ 225	$ 117	$ 225	$ 110