Reinsurance - Credit Quality Information (Details) - USD ($) $ in Millions	Jun. 30, 2023	Mar. 31, 2023	Dec. 31, 2022	Jun. 30, 2022	Mar. 31, 2022	Dec. 31, 2021	Jan. 01, 2021
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 7,022		$ 7,069
Reinsurance Recoverable, Allowance for Credit Loss	(110)		(105)	$ (105)
Net Reinsurance Recoverables	6,912		6,964			$ 6,524	$ 6,013
Mandatory and Voluntary Risk Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	207		218
Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	304		319
Other not rated companies [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	211		284
AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	6,300		6,248
AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,173		2,094
AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,534		2,667
AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	893		764
AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	76		85
AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	604		618
AM Best, Below B plus plus Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	20		20
Corporate
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	250		261
Reinsurance Recoverable, Allowance for Credit Loss	(2)		(2)	(2)
Net Reinsurance Recoverables	248		259
Corporate | Mandatory and Voluntary Risk Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | Other not rated companies [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	250		261
Corporate | AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	247		259
Corporate | AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Corporate | AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	3		2
Corporate | AM Best, Below B plus plus Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	6,522		6,557
Reinsurance Recoverable, Allowance for Credit Loss	(107)	$ (102)	(102)	(102)	$ (96)	(96)
Net Reinsurance Recoverables	6,415		6,455
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Mandatory and Voluntary Risk Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	207		218
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	304		319
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Other not rated companies [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	205		279
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Reinsurance Contract [Axis]: Before Disputed Amounts [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(45)	(44)	(42)	(41)	(40)	(42)
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(62)	$ (58)	(60)	(61)	$ (56)	$ (54)
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	5,806		5,741
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,173		2,094
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,049		2,169
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	893		763
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	70		79
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	601		616
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AM Best, Below B plus plus Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	20		20
Group Benefits | Operating Segments [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	250		251
Reinsurance Recoverable, Allowance for Credit Loss	(1)		(1)	$ (1)
Net Reinsurance Recoverables	249		250
Group Benefits | Operating Segments [Member] | Mandatory and Voluntary Risk Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Group Benefits | Operating Segments [Member] | Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Group Benefits | Operating Segments [Member] | Other not rated companies [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	6		5
Group Benefits | Operating Segments [Member] | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	244		246
Group Benefits | Operating Segments [Member] | AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Group Benefits | Operating Segments [Member] | AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	238		239
Group Benefits | Operating Segments [Member] | AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		1
Group Benefits | Operating Segments [Member] | AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	6		6
Group Benefits | Operating Segments [Member] | AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	0		0
Group Benefits | Operating Segments [Member] | AM Best, Below B plus plus Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 0		$ 0