Fair Value Measurements - Changes in Level 3 Recurring Fair Value Measurements, Liabilities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Derivative liabilities, net:
Fair Value Beginning of Year	$ (28)	$ (479)	$ (512)
Net Realized and Unrealized (Gains) Losses Included in Income	114	311
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	302	(278)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	35	0
Fair Value End of Period	(28)	(479)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(27)	(96)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 0	$ 0
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Adjusted Revenues	Adjusted Revenues
Fair Value, Liability, Recurring Basis, Unobservable Input Reconciliation, Liability, Gain (Loss), Statement of Other Comprehensive Income or Comprehensive Income [Extensible Enumeration]	Other comprehensive income (loss)	Other comprehensive income (loss)
Net realized gains/(losses)
Derivative liabilities, net:
Fair Value, Liability, Recurring Basis, Still Held, Unrealized Gain (Loss), Statement of Income or Comprehensive Income [Extensible Enumeration]	Total net realized gains (losses)	Total net realized gains (losses)
Derivative liabilities, net
Derivative liabilities, net:
Fair Value Beginning of Year	$ (453)	$ (583)
Net Realized and Unrealized (Gains) Losses Included in Income	41	28
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	377	102
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	35	0
Fair Value End of Year	0	(453)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	55
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Net Realized and Unrealized (Gains) Losses Included in Income	41	28
Interest rate contracts
Derivative liabilities, net:
Fair Value Beginning of Year	(406)	(311)
Net Realized and Unrealized (Gains) Losses Included in Income	61	(44)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	345	(51)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Year	0	(406)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	37
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Foreign exchange contracts
Derivative liabilities, net:
Fair Value Beginning of Year	2	0
Net Realized and Unrealized (Gains) Losses Included in Income	(2)	2
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Year	0	2
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	(2)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Equity contracts
Derivative liabilities, net:
Fair Value Beginning of Year	(48)	(271)
Net Realized and Unrealized (Gains) Losses Included in Income	(18)	72
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	31	151
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	35	0
Fair Value End of Year	0	(48)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	19
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Credit contracts
Derivative liabilities, net:
Fair Value Beginning of Year	0	0
Net Realized and Unrealized (Gains) Losses Included in Income	1	0
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	0	0
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	(1)	0
Fair Value End of Year	0	0
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(1)	(1)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other contracts
Derivative liabilities, net:
Fair Value Beginning of Year	(1)	(1)
Net Realized and Unrealized (Gains) Losses Included in Income	(1)	(2)
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	1	2
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	1	0
Fair Value End of Year	0	(1)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	2
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Fortitude Re funds withheld payable
Derivative liabilities, net:
Fair Value Beginning of Year	(128)	(148)	(41)
Net Realized and Unrealized (Gains) Losses Included in Income	75	273
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(55)	(380)
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	(128)	(148)
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	(26)	(151)
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	0	0
Other Liabilities
Derivative liabilities, net:
Fair Value Beginning of Year	100	122	$ 112
Net Realized and Unrealized (Gains) Losses Included in Income	(2)	10
Other Comprehensive Income (Loss)	0	0
Purchases, Sales, Issuances and Settlements, Net	(20)	0
Gross Transfers In	0	0
Gross Transfers Out	0	0
Other	0	0
Fair Value End of Period	100	122
Changes in Unrealized Gains (Losses) Included in Income on Instruments Held at End of Period	0	0
Changes in Unrealized Gains (Losses) Included in Other Comprehensive Income (Loss) for Recurring Level 3 Instruments Held at End of Period	$ 0	$ 0