Reinsurance - Reinsurance Recoverable, Allowance for Credit Loss (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	$ 99	$ 108
Reinsurance Recoverable, Credit Loss Expense (Reversal)	(2)	(13)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	99	98
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	105
Reinsurance Recoverable, Credit Loss Expense (Reversal)	(2)	(13)
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	96	95
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
Disputes [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	54	53
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	56	56
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	54	53
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	56	56
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
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
Before Uncollectible Reinsurance
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss, Beginning Balance	45	55
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	43	42
Before Uncollectible Reinsurance | 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	52
Reinsurance Recoverable, Allowance for Credit Loss, Ending Balance	40	39
Before Uncollectible Reinsurance | 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
Before Uncollectible Reinsurance | 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