Insurance Liabilities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Jan. 20, 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contractual deductible recoverable amount	$ 12,500		$ 12,100
Collateral held for deductible recoverable amounts	8,800		8,700
Liability for unpaid losses and loss adjustment expenses, allowance for credit losses	14		14
Favorable prior year loss development	0	$ 27
Net loss reserve discount	$ 1,212		1,233
Tabular discount rate (as a percent)	45.00%
Workers compensation tabular discount amount	$ 293		294
Workers compensation non tabular discount amount	919		$ 939
Net loss reserve discount charge	$ (76)	(64)
New York
Liability for Future Policy Benefit, by Product Segment [Line Items]
Nontabular discount rate (as a percent)	5.00%
NICO
Liability for Future Policy Benefit, by Product Segment [Line Items]
Amortization of deferred gain on retroactive reinsurance	$ 27	53
Term Life Insurance
Liability for Future Policy Benefit, by Product Segment [Line Items]
(Decrease) increase in reserves	$ (1)	$ 7
U.S. Run-Off Long Tail Insurance Lines | NICO | Accident Years 2015 and Prior
Liability for Future Policy Benefit, by Product Segment [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