Reinsurance - Reinsurance Recoverable, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2023	Jun. 30, 2022	Jun. 30, 2023	Jun. 30, 2022
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			$ 105
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	$ 110	$ 105	110	$ 105
Operating Segments [Member] | Property, Liability and Casualty Insurance Product Line
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	102	96	102	96
Reinsurance Recoverable, Credit Loss Expense (Reversal)	1	1	3	(1)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	107	102	107	102
Operating Segments [Member] | Group Benefits
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			1
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	1	1	1	1
Corporate, Non-Segment [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			2
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	2	2	2	2
Reinsurance Contract [Axis]: Before Disputed Amounts [Member] | Operating Segments [Member] | Property, Liability and Casualty Insurance Product Line
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	44	40	42	42
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	45	41	45	41
Reinsurance Contract [Axis]: Disputes [Member] | Operating Segments [Member] | Property, Liability and Casualty Insurance Product Line
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	58	56	60	54
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	$ 62	$ 61	$ 62	$ 61