Insurance Liabilities - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2024	Sep. 30, 2023	Sep. 30, 2024	Sep. 30, 2023	Dec. 31, 2023	Jan. 20, 2017
Liability for Future Policy Benefit, by Product Segment [Line Items]
Contractual deductible recoverable amount	$ 12,800		$ 12,800		$ 12,100
Collateral held for deductible recoverable amounts	8,600		8,600		8,700
Liability for unpaid losses and loss adjustment expenses, allowance for credit losses	14		14		14
Favorable prior year loss development	(187)	$ 246	(79)	$ 380
Net loss reserve discount	1,202		$ 1,202		1,233
Tabular discount rate (as a percent)			45.00%
Workers compensation tabular discount amount	280		$ 280		294
Workers compensation non tabular discount amount	922		922		$ 939
Net loss reserve discount charge	29	5	$ 131	85
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	$ 209	$ (36)	$ 230	$ 36
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