Expected Loss to be Paid (Recovered) - Net Expected Loss to be Paid (Recovered) Roll Forward (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2023	Dec. 31, 2022	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	$ 522	$ 411	$ 529
Accretion of discount	20	16	7
Changes in discount rates	3	(115)	(33)
Changes in timing and assumptions	141	(26)	(261)
Total economic loss development (benefit)	164	(125)	(287)
Net (paid) recovered losses	(181)	236	169
Net expected loss to be paid (recovered), end of period	$ 505	$ 522	411
Weighted average risk free discount rate	4.10%	4.08%
Period after the end of the reporting period within which the ceded paid losses are typically settled (in days)	45 days
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	$ 110	$ 202	188
Total economic loss development (benefit)	(48)	(142)	(83)
Net (paid) recovered losses	25	50	97
Net expected loss to be paid (recovered), end of period	87	110	202
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	412	209	341
Total economic loss development (benefit)	212	17	(204)
Net (paid) recovered losses	(206)	186	72
Net expected loss to be paid (recovered), end of period	418	412	209
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	44	52	40
Total economic loss development (benefit)	8	1	17
Net (paid) recovered losses	(8)	(9)	(5)
Net expected loss to be paid (recovered), end of period	$ 44	$ 44	52
U.S.
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Percent of total non-U.S. net expected losses to paid	96.10%	98.50%
U.S. | RMBS
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	$ 66	$ 150	148
Total economic loss development (benefit)	(56)	(143)	(100)
Net (paid) recovered losses	33	59	102
Net expected loss to be paid (recovered), end of period	43	66	150
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	403	197	305
Total economic loss development (benefit)	201	19	(182)
Net (paid) recovered losses	(206)	187	74
Net expected loss to be paid (recovered), end of period	398	403	197
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	9	12	36
Total economic loss development (benefit)	11	(2)	(22)
Net (paid) recovered losses	0	(1)	(2)
Net expected loss to be paid (recovered), end of period	$ 20	$ 9	$ 12
Minimum
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Risk free discount rate	3.79%	3.82%
Maximum
Present Value of Net Expected Loss and Loss Adjustment Expenses to be Paid [Roll Forward]
Risk free discount rate	5.40%	4.69%