Insurance Liabilities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025	Dec. 31, 2025	Jan. 20, 2017
Liability for Future Policy Benefit, Activity [Line Items]
Contractual deductible recoverable amount	$ 14,000		$ 13,800
Collateral held for deductible recoverable amounts	10,000		9,600
Liability for unpaid losses and loss adjustment expenses, allowance for credit losses	14		14
Unfavorable (favorable) prior year loss reserve development	(126)	$ (33)
Net loss reserve discount	$ 1,273		$ 1,172
Discount and spread, ceiling (as a percent)	4.50%
Discount and spread (as a percent)	4.50%		4.50%
Tabular discount rate (as a percent)	45.00%
Workers compensation tabular discount amount	$ 149		$ 141
Workers compensation non tabular discount amount	1,100		$ 1,000
Net loss reserve discount benefit (charge)	$ 48	(17)
New York
Liability for Future Policy Benefit, Activity [Line Items]
Nontabular discount rate (as a percent)	5.00%
NICO
Liability for Future Policy Benefit, Activity [Line Items]
Amortization of deferred gain on retroactive reinsurance	$ 20	$ 17
U.S. Run-Off Long Tail Insurance Lines | NICO | Accident Years 2015 and Prior
Liability for Future Policy Benefit, Activity [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
Long-Duration Insurance
Liability for Future Policy Benefit, Activity [Line Items]
Ceded percentage	1		1
Ceded reserves	$ 727		$ 797
Other reserves	$ 554		$ 583