Acquisitions and Sale of Businesses - Assets and liabilities disposed (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Jun. 30, 2021	Dec. 31, 2020	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and investments			$ 14,512	$ 15,745
Recoverables from reinsurers			3,977	3,519
Prepaid reinsurance premiums			917	834
Agents’ balances and premiums receivable			1,339	1,265
Other assets			1,219	902
Total assets			28,831	28,931
Unpaid losses and loss adjustment expenses		$ 10,392	11,974	11,074	$ 10,392	$ 10,232
Unearned premiums			3,246	3,041
Payable to reinsurers			1,035	920
Other liabilities			1,696	1,700
Total liabilities			24,779	23,919
Realized gains on subsidiaries			$ 0	$ 4	23
Neon Capital Limited
Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Sale proceeds, net of expenses					3
Cash and investments		453			453
Recoverables from reinsurers		224			224
Prepaid reinsurance premiums		8			8
Agents’ balances and premiums receivable		42			42
Other assets		60			60
Total assets		787			787
Unpaid losses and loss adjustment expenses		640			640
Unearned premiums		49			49
Payable to reinsurers		19			19
Other liabilities		92			92
Total liabilities		800			800
Reclassification from accumulated other comprehensive income					(7)
Net liabilities of businesses sold		(20)			(20)
Realized gains on subsidiaries	$ 4	$ 23			$ 23