Fair Value Measurement - Financial Instruments Carried at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2024	Dec. 31, 2023
Assets:
Fixed-maturity securities, available-for-sale	$ 6,369	$ 6,307
Fixed-maturity securities, trading, at fair value	147	318
Short-term investments, at fair value	1,221	1,661
Other invested assets	926	829
FG VIEs’ assets	147	174
Other assets	131	123
Liabilities:
Liabilities of CIVs	164	554
Obligations of state and political subdivisions
Assets:
Fixed-maturity securities, available-for-sale	1,940	2,661
U.S. government and agencies
Assets:
Fixed-maturity securities, available-for-sale	67	60
Corporate securities
Assets:
Fixed-maturity securities, available-for-sale	2,382	2,141
RMBS
Assets:
Fixed-maturity securities, available-for-sale	567	342
CMBS
Assets:
Fixed-maturity securities, available-for-sale	186	151
Non-U.S. government securities
Assets:
Fixed-maturity securities, available-for-sale	69	100
Recurring
Assets:
Other invested assets	4	3
Other assets	131	123
Total assets carried at fair value	8,118	8,917
Liabilities:
Other liabilities	34	53
Total liabilities carried at fair value	198	607
Recurring | Financial Guaranty Variable Interest Entities
Liabilities:
Liabilities of CIVs	164	554
Recurring | Financial Guaranty Variable Interest Entities
Assets:
FG VIEs’ assets	147	174
Recurring | Consolidated investment vehicles
Assets:
FG VIEs’ assets		331
Recurring | Level 1
Assets:
Other invested assets	0	0
Other assets	65	55
Total assets carried at fair value	1,283	1,712
Liabilities:
Other liabilities	0	0
Total liabilities carried at fair value	0	0
Recurring | Level 1 | Financial Guaranty Variable Interest Entities
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 1 | Financial Guaranty Variable Interest Entities
Assets:
FG VIEs’ assets	0	0
Recurring | Level 1 | Consolidated investment vehicles
Assets:
FG VIEs’ assets		0
Recurring | Level 2
Assets:
Other invested assets	0	0
Other assets	59	52
Total assets carried at fair value	5,387	5,780
Liabilities:
Other liabilities	0	0
Total liabilities carried at fair value	0	0
Recurring | Level 2 | Financial Guaranty Variable Interest Entities
Liabilities:
Liabilities of CIVs	0	0
Recurring | Level 2 | Financial Guaranty Variable Interest Entities
Assets:
FG VIEs’ assets	0	0
Recurring | Level 2 | Consolidated investment vehicles
Assets:
FG VIEs’ assets		62
Recurring | Level 3
Assets:
Other invested assets	4	3
Other assets	7	16
Total assets carried at fair value	1,448	1,425
Liabilities:
Other liabilities	34	53
Total liabilities carried at fair value	198	607
Recurring | Level 3 | Financial Guaranty Variable Interest Entities
Liabilities:
Liabilities of CIVs	164	554
Recurring | Level 3 | Financial Guaranty Variable Interest Entities
Assets:
FG VIEs’ assets	147	174
Recurring | Level 3 | Consolidated investment vehicles
Assets:
FG VIEs’ assets		269
Fixed-maturity securities | Recurring
Assets:
Fixed-maturity securities, available-for-sale	6,369	6,307
Fixed-maturity securities, trading, at fair value	147	318
Fixed-maturity securities | Recurring | Obligations of state and political subdivisions
Assets:
Fixed-maturity securities, available-for-sale	1,940	2,661
Fixed-maturity securities | Recurring | U.S. government and agencies
Assets:
Fixed-maturity securities, available-for-sale	67	60
Fixed-maturity securities | Recurring | Corporate securities
Assets:
Fixed-maturity securities, available-for-sale	2,382	2,141
Fixed-maturity securities | Recurring | RMBS
Assets:
Fixed-maturity securities, available-for-sale	567	342
Fixed-maturity securities | Recurring | CMBS
Assets:
Fixed-maturity securities, available-for-sale	186	151
Fixed-maturity securities | Recurring | Asset-backed securities
Assets:
Fixed-maturity securities, available-for-sale	1,158	852
Fixed-maturity securities | Recurring | Non-U.S. government securities
Assets:
Fixed-maturity securities, available-for-sale	69	100
Fixed-maturity securities | Recurring | Level 1
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities, trading, at fair value	0	0
Fixed-maturity securities | Recurring | Level 1 | Obligations of state and political subdivisions
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | U.S. government and agencies
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | Corporate securities
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | RMBS
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | CMBS
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | Asset-backed securities
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 1 | Non-U.S. government securities
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 2
Assets:
Fixed-maturity securities, available-for-sale	5,183	5,344
Fixed-maturity securities, trading, at fair value	142	318
Fixed-maturity securities | Recurring | Level 2 | Obligations of state and political subdivisions
Assets:
Fixed-maturity securities, available-for-sale	1,930	2,655
Fixed-maturity securities | Recurring | Level 2 | U.S. government and agencies
Assets:
Fixed-maturity securities, available-for-sale	67	60
Fixed-maturity securities | Recurring | Level 2 | Corporate securities
Assets:
Fixed-maturity securities, available-for-sale	2,382	2,141
Fixed-maturity securities | Recurring | Level 2 | RMBS
Assets:
Fixed-maturity securities, available-for-sale	422	188
Fixed-maturity securities | Recurring | Level 2 | CMBS
Assets:
Fixed-maturity securities, available-for-sale	186	151
Fixed-maturity securities | Recurring | Level 2 | Asset-backed securities
Assets:
Fixed-maturity securities, available-for-sale	127	49
Fixed-maturity securities | Recurring | Level 2 | Non-U.S. government securities
Assets:
Fixed-maturity securities, available-for-sale	69	100
Fixed-maturity securities | Recurring | Level 3
Assets:
Fixed-maturity securities, available-for-sale	1,186	963
Fixed-maturity securities, trading, at fair value	5	0
Fixed-maturity securities | Recurring | Level 3 | Obligations of state and political subdivisions
Assets:
Fixed-maturity securities, available-for-sale	10	6
Fixed-maturity securities | Recurring | Level 3 | U.S. government and agencies
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 3 | Corporate securities
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 3 | RMBS
Assets:
Fixed-maturity securities, available-for-sale	145	154
Fixed-maturity securities | Recurring | Level 3 | CMBS
Assets:
Fixed-maturity securities, available-for-sale	0	0
Fixed-maturity securities | Recurring | Level 3 | Asset-backed securities
Assets:
Fixed-maturity securities, available-for-sale	1,031	803
Fixed-maturity securities | Recurring | Level 3 | Non-U.S. government securities
Assets:
Fixed-maturity securities, available-for-sale	0	0
Short-term investments | Recurring
Assets:
Fixed-maturity securities, available-for-sale		1,661
Short-term investments, at fair value	1,221
Short-term investments | Recurring | Level 1
Assets:
Fixed-maturity securities, available-for-sale		1,657
Short-term investments, at fair value	1,218
Short-term investments | Recurring | Level 2
Assets:
Fixed-maturity securities, available-for-sale		4
Short-term investments, at fair value	3
Short-term investments | Recurring | Level 3
Assets:
Fixed-maturity securities, available-for-sale		0
Short-term investments, at fair value	0
Fund Investments | Recurring | Assets of CIVs, equity securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets	99
Fund Investments | Recurring | Equity Securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets		83
Fund Investments | Recurring | Structured products | Consolidated investment vehicles
Assets:
FG VIEs’ assets		248
Fund Investments | Recurring | Level 1 | Assets of CIVs, equity securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets	0
Fund Investments | Recurring | Level 1 | Equity Securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets		0
Fund Investments | Recurring | Level 1 | Structured products | Consolidated investment vehicles
Assets:
FG VIEs’ assets		0
Fund Investments | Recurring | Level 2 | Assets of CIVs, equity securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets	0
Fund Investments | Recurring | Level 2 | Equity Securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets		3
Fund Investments | Recurring | Level 2 | Structured products | Consolidated investment vehicles
Assets:
FG VIEs’ assets		59
Fund Investments | Recurring | Level 3 | Assets of CIVs, equity securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets	$ 99
Fund Investments | Recurring | Level 3 | Equity Securities | Consolidated investment vehicles
Assets:
FG VIEs’ assets		80
Fund Investments | Recurring | Level 3 | Structured products | Consolidated investment vehicles
Assets:
FG VIEs’ assets		$ 189