Reserve for Unpaid Losses and Loss Adjustment Expenses - PC Additional Information (Details) - USD ($) $ in Millions		12 Months Ended				60 Months Ended
	May 23, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2016	Dec. 31, 2021	Dec. 31, 2018
Liability for Claims and Claims Adjustment Expense [Line Items]
Benefits, losses and loss adjustment expenses		$ 12,729	$ 11,805	$ 11,472
Unpaid losses and loss adjustment expenses		39,659	37,855			$ 39,659
us-gaap_SupplementalInformationForPropertyCasualtyInsuranceUnderwritersPriorYearClaimsAndClaimsAdjustmentExpense_BSASettlement		650
Reinsurance premium		0	0	91
Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Liability for Asbestos and Environmental Claims, Gross, Period Increase (Decrease)		155	218
Prior accident year development [1]			218
Change in Deferred Gain on Retroactive Reinsurance		155	210
Adverse development from comprehensive annual review			220			1,015
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		485
Reinsurance Retention Policy, Amount Retained					$ 1,700
Net asbestos reserves
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]		106	127
Net environmental reserves
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]		49	91
Adverse Development Cover Navigators Group [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in Deferred Gain on Retroactive Reinsurance		91	102	16
Adverse development from comprehensive annual review		300
Reinsurance premium	$ 91
Deferred Revenue		209				209
Adverse Development Cover Navigators Group [Member] | Remaining [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		0
Adverse Development Cover Navigators Group [Member] | Retention Layer for Reserve for the Covered Liabilities as of the Inception Date [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Amount Retained		1,816
Adverse Development Cover Navigators Group [Member] | Retention Layer Above Reserve for the Covered Liabilities as of the Inception Date [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Amount Retained		100
Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Adverse development from comprehensive annual review			220
Benefits, losses and loss adjustment expenses			2
Asbestos and Environmental | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Adverse development from comprehensive annual review		1,015
Reinsurance premium					650
Reinsurance Retention Policy, Amount Retained					$ 1,700
Deferred Revenue		365				365
Asbestos and Environmental | Remaining [Member] | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		485
Liability | Abuse Claims [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]			254
Unpaid losses and loss adjustment expenses		787				787
Liability | Adverse Development Cover Navigators Group [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Adverse development from comprehensive annual review		86
Property and Casualty Insurance Subsidiaries
Liability for Claims and Claims Adjustment Expense [Line Items]
Prior accident year development [1]		199	(136)	(65)
Adverse development from comprehensive annual review		1,243	1,156	826
Unpaid losses and loss adjustment expenses		31,449	29,622	28,261		$ 31,449	$ 24,584
Property and Casualty Insurance Subsidiaries | Adverse Development Cover Navigators Group [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Change in Deferred Gain on Retroactive Reinsurance		246	$ 312	$ 16
Automobile | Adverse Development Cover Navigators Group [Member] | P&C Commercial Lines
Liability for Claims and Claims Adjustment Expense [Line Items]
Adverse development from comprehensive annual review		16
Maximum | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		1,500
Maximum | Adverse Development Cover Navigators Group [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		300
Maximum | Asbestos and Environmental | Asbestos and Environmental
Liability for Claims and Claims Adjustment Expense [Line Items]
Reinsurance Retention Policy, Excess Retention, Amount Reinsured		$ 1,500
Maximum | Property and Casualty Insurance Subsidiaries
Liability for Claims and Claims Adjustment Expense [Line Items]
Weighted average discount rate		14.03%	14.03%	14.03%		14.03%
Minimum [Member] | Property and Casualty Insurance Subsidiaries
Liability for Claims and Claims Adjustment Expense [Line Items]
Weighted average discount rate		0.83%	0.83%	1.76%		0.83%
PG&E [Member]
Liability for Claims and Claims Adjustment Expense [Line Items]
Former Gain Contingency, Recognized in Current Period			$ 289