Reinsurance - Reinsurance Recoverable, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2023	Sep. 30, 2022
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			$ 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	$ 107	$ 102	102	$ 96
Reinsurance Recoverable, Credit Loss Expense (Reversal)	1	1	4	0
Operating Segments [Member] | Group Benefits
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			1
Corporate, Non-Segment [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance			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	45	41	42	42
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	$ 62	$ 61	$ 60	$ 54