Amount of increase in allowance for credit loss on reinsurance recoverable, from recovery.

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Amount of allowance for credit loss on reinsurance recoverable.

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Reinsurance - Reinsurance Recoverable, ACL (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	$ 55		$ 48
Reinsurance Recoverable, Credit Loss Expense (Reversal)	4
Reinsurance Recoverable, Allowance for Credit Loss, Recovery	1
Corporate
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	2		0
Reinsurance Recoverable, Credit Loss Expense (Reversal)	1
Reinsurance Recoverable, Allowance for Credit Loss, Recovery	0
Operating Segments \| Property and Casualty Insurance Subsidiaries
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	52		48
Reinsurance Recoverable, Credit Loss Expense (Reversal)	3
Reinsurance Recoverable, Allowance for Credit Loss, Recovery	1
Operating Segments \| Group Insurance Policy [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	1		0
Reinsurance Recoverable, Credit Loss Expense (Reversal)	0
Reinsurance Recoverable, Allowance for Credit Loss, Recovery	0
Uncollectible reinsurance
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	108		114
Uncollectible reinsurance \| Corporate
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	2		0
Uncollectible reinsurance \| Operating Segments \| Property and Casualty Insurance Subsidiaries
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	105		114
Uncollectible reinsurance \| Operating Segments \| Group Insurance Policy [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	1		0
Disputes [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	53		66
Disputes [Member] \| Corporate
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	0		0
Disputes [Member] \| Operating Segments \| Property and Casualty Insurance Subsidiaries
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	53		66
Disputes [Member] \| Operating Segments \| Group Insurance Policy [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss	$ 0		0
Cumulative Effect, Period of Adoption, Adjustment [Member] \| Accounting Standards Update 2016-13 [Member]
Reinsurance Recoverable, Past Due [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			2
Cumulative Effect, Period of Adoption, Adjustment [Member] \| Accounting Standards Update 2016-13 [Member] \| Corporate
Reinsurance Recoverable, Past Due [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			1
Cumulative Effect, Period of Adoption, Adjustment [Member] \| Accounting Standards Update 2016-13 [Member] \| Operating Segments \| Property and Casualty Insurance Subsidiaries
Reinsurance Recoverable, Past Due [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			0
Cumulative Effect, Period of Adoption, Adjustment [Member] \| Accounting Standards Update 2016-13 [Member] \| Operating Segments \| Group Insurance Policy [Member]
Reinsurance Recoverable, Past Due [Line Items]
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest			1
Cumulative Effect, Period of Adoption, Adjusted Balance [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss			50
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] \| Corporate
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss			1
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] \| Operating Segments \| Property and Casualty Insurance Subsidiaries
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss			48
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] \| Operating Segments \| Group Insurance Policy [Member]
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss			$ 1
Cumulative Effect, Period of Adoption, Adjusted Balance [Member] \| Uncollectible reinsurance
Reinsurance Recoverable, Allowance for Credit Loss [Roll Forward]
Reinsurance Recoverable, Allowance for Credit Loss		$ 116