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
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
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	$ 432	$ 472	$ 411	$ 529
Accretion of discount	3	2	5	3
Changes in discount rates	(42)	15	(89)	(33)
Changes in timing and assumptions	7	(37)	8	23
Total economic loss development (benefit)	(32)	(20)	(76)	(7)
Net (paid) recovered losses	42	14	107	(56)
Net expected loss to be paid (recovered), end of period	442	466	$ 442	466
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)			45 days
Loss and LAE Reserve paid	7	6	$ 20	10
Expected LAE to be paid	14		14		$ 26
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	191	252	209	341
Total economic loss development (benefit)	6	0	(44)	3
Net (paid) recovered losses	20	(9)	52	(101)
Net expected loss to be paid (recovered), end of period	217	243	217	243
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	181	228	197	305
Total economic loss development (benefit)	8	1	(40)	16
Net (paid) recovered losses	21	(8)	53	(100)
Net expected loss to be paid (recovered), end of period	210	221	210	221
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	10	24	12	36
Total economic loss development (benefit)	(2)	(1)	(4)	(13)
Net (paid) recovered losses	(1)	(1)	(1)	(1)
Net expected loss to be paid (recovered), end of period	7	22	7	22
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	195	181	150	148
Total economic loss development (benefit)	(39)	(28)	(32)	(17)
Net (paid) recovered losses	23	25	61	47
Net expected loss to be paid (recovered), end of period	179	178	179	178
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	46	39	52	40
Total economic loss development (benefit)	1	8	0	7
Net (paid) recovered losses	(1)	(2)	(6)	(2)
Net expected loss to be paid (recovered), end of period	46	45	46	45
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	241	220	202	188
Total economic loss development (benefit)	(38)	(20)	(32)	(10)
Net (paid) recovered losses	22	23	55	45
Net expected loss to be paid (recovered), end of period	$ 225	$ 223	$ 225	$ 223