Insurance Liabilities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2025	Mar. 31, 2024	Dec. 31, 2024	Jan. 20, 2017
Liabilities for Guarantees on Long-Duration Contracts [Line Items]
Contractual deductible recoverable amount	$ 12,100		$ 12,100
Collateral held for deductible recoverable amounts	8,700		8,600
Liability for unpaid losses and loss adjustment expenses, allowance for credit losses	14		14
Unfavorable (favorable) prior year loss reserve development	(33)	$ 0
Net loss reserve discount	$ 1,159		1,175
Tabular discount rate (as a percent)	45.00%
Workers compensation tabular discount amount	$ 112		107
Workers compensation non tabular discount amount	1,000		$ 1,100
Net loss reserve discount charge	$ (17)	(76)
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	$ 17	$ 27
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%
Ceded to NICO percent of paid losses (as a percent)				80.00%
Ceded to NICO net paid losses in excess				$ 25,000
Ceded to NICO net paid losses in excess, aggregate limit				25,000
NICO's limit of liability under the contract				20,000
Consideration paid, including interest				$ 10,200