Reinsurance - Reinsurance Recoverable, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	$ 99	$ 98	$ 99	$ 108
Reinsurance Recoverable, Credit Loss Expense (Reversal)	1	1	(1)	(12)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	105	99	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	96	95	96	105
Reinsurance Recoverable, Credit Loss Expense (Reversal)	1	1	(1)	(12)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	102	96	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	1	1
Reinsurance Recoverable, Credit Loss Expense (Reversal)	0	0	0	0
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	2	2	2
Reinsurance Recoverable, Credit Loss Expense (Reversal)	0	0	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	2	2	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	43	42	45	55
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	44	43	44	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	40	39	42	52
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	41	40	41	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	1	1
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	1	1	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	2	2
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	2	2	2	2
Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	56	56	54	53
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	61	56	61	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	56	56	54	53
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	61	56	61	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	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	0	0	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	0	0
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	$ 0	$ 0	$ 0	$ 0