Insurance Liabilities - Narrative (Details) $ in Millions	12 Months Ended
	Dec. 31, 2025 USD ($)	Dec. 31, 2024 USD ($)	Dec. 31, 2023 USD ($)	Jan. 20, 2017
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Contractual deductible recoverable amount	$ 13,800	$ 12,100
Collateral held for deductible recoverable amounts	9,600	8,600
Liability for unpaid losses and loss adjustment expenses, allowance for credit losses	14	14
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(216)
Unfavorable (favorable) prior year loss reserve development	(216)	254	$ (392)
Net loss reserve discount	$ 1,172	1,175
Discount and spread, ceiling (as a percent)	4.50%
Discount and spread (as a percent)	4.50%
Tabular discount rate (as a percent)	45.00%
Workers compensation tabular discount amount	$ 141	107
Workers compensation non tabular discount amount	1,000	1,100
Net loss reserve discount charge	$ (48)	(226)	(195)
New York
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Nontabular discount rate (as a percent)	5.00%
NICO
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Amortization of deferred gain on retroactive reinsurance	$ 158	$ 322	48
U.S. Run-Off Long Tail Insurance Lines | NICO | Accident Years 2015 and Prior
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Risk Transferred - U.S. Commercial long-tail exposures for accident years 2015 and prior (as a percent)				80.00%
Long-Duration Insurance
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Ceded percentage	1	1
Ceded reserves	$ 797	$ 691
Other reserves	583	621
Businesses in run-off
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	106	196
Businesses in run-off | Blackboard
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions		112
Businesses in run-off | Asbestos Loss Portfolio Transfer
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions		85
U.S. Personal Insurance
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(11)	(23)	(64)
UK/Europe Casualty and Financial lines
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	216	170	165
UK/Europe Property and Special Risks
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(18)	(35)	81
UK/Europe and Japan Personal Insurance
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	38	(47)	(57)
Other product lines
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(469)	(299)	(162)
U.S. Workers' Compensation (before discount)
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(133)	(273)	(267)
U.S. Excess Casualty
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	303	545	(32)
U.S. Other Casualty
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(92)	12	(133)
U.S. Financial Lines
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	(38)	51	94
U.S. Property and Special Risks
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Unfavorable (favorable) prior year development, net of external reinsurance, before ADC cessions	$ (118)	$ (44)	$ (10)