Reinsurance - Reinsurance Recoverable, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	$ 105	$ 99
Reinsurance Recoverable, Credit Loss Expense (Reversal)	2	(2)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	105	99
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
Reinsurance Recoverable, Credit Loss Expense (Reversal)	2	(2)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	102	96
Operating Segments [Member] | Group Benefits
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	1	1
Reinsurance Recoverable, Credit Loss Expense (Reversal)	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	1	1
Corporate, Non-Segment [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	2	2
Reinsurance Recoverable, Credit Loss Expense (Reversal)	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	2	2
Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	45	45
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	47	43
Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [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	42	42
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	44	40
Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member] | Operating Segments [Member] | Group Benefits
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	1	1
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	1	1
Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member] | Corporate, Non-Segment [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	2	2
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	2	2
Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	60	54
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	58	56
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	60	54
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	58	56
Reinsurance Contract [Axis]: Disputes [Member] | Operating Segments [Member] | Group Benefits
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	0	0
Reinsurance Contract [Axis]: Disputes [Member] | Corporate, Non-Segment [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	$ 0	$ 0