Reserve for Unpaid Losses and Loss Adjustment Expenses - P&C Liabilities for Unpaid Losses and Loss Adjustment Expenses (Details) - USD ($) $ in Millions	3 Months Ended	7 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross			$ 37,855
Payments
Ending liabilities for unpaid losses and loss adjustment expenses, gross			39,659	$ 37,855
Adverse Development Cover Navigators Group [Member]
Provision for unpaid losses and loss adjustment expenses
Increase (Decrease) in Deferred Revenue			(91)	(102)	$ (16)
Property and Casualty Insurance Subsidiaries
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Beginning liabilities for unpaid losses and loss adjustment expenses, gross			29,622	28,261	24,584
Reinsurance Recoverable for Unpaid Claims and Claims Adjustments		$ 5,275	6,081	5,725	5,275	$ 4,232
Beginning liabilities for unpaid losses and loss adjustment expenses, net			23,897	22,986	20,352
Provision for unpaid losses and loss adjustment expenses
Current accident year			7,911	7,794	7,463
Prior accident year development [1]			199	(136)	(65)
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims			8,110	7,658	7,398
Payments
Current accident year			(2,276)	(2,214)	(2,374)
Prior accident years			(4,119)	(4,190)	(4,374)
Total payments			(6,395)	(6,404)	(6,748)
Foreign currency adjustment			2	14	(1)
Unpaid Losses and Loss Adjustment Expenses, Net of Reinsurance		22,986	25,368	23,897	22,986	$ 20,352
Ending liabilities for unpaid losses and loss adjustment expenses, gross		28,261	31,449	29,622	28,261
Property and Casualty Insurance Subsidiaries | Continental Europe Operations [Member]
Payments
Net change in reserves transferred to liabilities held for sale		0	0	(45)	0
Property and Casualty Insurance Subsidiaries | Adverse Development Cover Navigators Group [Member]
Provision for unpaid losses and loss adjustment expenses
Increase (Decrease) in Deferred Revenue			(246)	(312)	(16)
The Navigators Group, Inc. [Member] | Adverse Development Cover Navigators Group [Member]
Provision for unpaid losses and loss adjustment expenses
Liability for Unpaid Claims and Claims Adjustment Expense, Incurred Claims	$ 97	97			84
Increase (Decrease) in Deferred Revenue		(16)
Payments
Current accident year	$ (29)
The Navigators Group, Inc. [Member] | Property and Casualty Insurance Subsidiaries
Liability for Unpaid Claims and Claims Adjustment Expense [Roll Forward]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Reserves net Reinsurance and Other Recoverables		$ 2,001	$ 0	$ 0	$ 2,001