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		9 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2022	Sep. 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	$ 442	$ 466	$ 411	$ 529
Accretion of discount	3	2	8	5
Changes in discount rates	(25)	(1)	(114)	(34)
Changes in timing and assumptions	(50)	(95)	(42)	(72)
Total economic loss development (benefit)	(72)	(94)	(148)	(101)
Net (paid) recovered losses (1)	357	(173)	464	(229)
Net expected loss to be paid (recovered), end of period	727	199	$ 727	199
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	5	5	$ 25	15
Expected LAE to be paid	11		11		$ 26
Puerto Rico | PRHTA
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Cash received	147		147
Notional amount of contingent value instrument received	672		672
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	217	243	209	341
Total economic loss development (benefit)	22	(31)	(22)	(28)
Net (paid) recovered losses (1)	393	(202)	445	(303)
Net expected loss to be paid (recovered), end of period	632	10	632	10
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	210	221	197	305
Total economic loss development (benefit)	24	(29)	(16)	(13)
Net (paid) recovered losses (1)	392	(201)	445	(301)
Net expected loss to be paid (recovered), end of period	626	(9)	626	(9)
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	7	22	12	36
Total economic loss development (benefit)	(2)	(2)	(6)	(15)
Net (paid) recovered losses (1)	1	(1)	0	(2)
Net expected loss to be paid (recovered), end of period	6	19	6	19
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	179	178	150	148
Total economic loss development (benefit)	(95)	(65)	(127)	(82)
Net (paid) recovered losses (1)	(32)	29	29	76
Net expected loss to be paid (recovered), end of period	52	142	52	142
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	45	52	40
Total economic loss development (benefit)	1	2	1	9
Net (paid) recovered losses (1)	(4)	0	(10)	(2)
Net expected loss to be paid (recovered), end of period	43	47	43	47
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	225	223	202	188
Total economic loss development (benefit)	(94)	(63)	(126)	(73)
Net (paid) recovered losses (1)	(36)	29	19	74
Net expected loss to be paid (recovered), end of period	$ 95	$ 189	$ 95	$ 189