Reinsurance - Credit Quality Information (Details) - USD ($) $ in Millions	Mar. 31, 2023	Dec. 31, 2022	Mar. 31, 2022	Dec. 31, 2021	Jan. 01, 2021
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	$ 7,035	$ 7,069
Reinsurance Recoverable, Allowance for Credit Loss	(105)	(105)	$ (99)	$ (99)
Net Reinsurance Recoverables	6,930	6,964		6,524	$ 6,013
Mandatory and Voluntary Risk Pools [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	217	218
Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	307	319
Other not rated companies [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	281	284
Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(47)	(45)	(43)	(45)
Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(58)	(60)	(56)	(54)
AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	6,230	6,248
AM Best, A++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,166	2,094
AM Best, A+ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	2,524	2,667
AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	817	764
AM Best, A- Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	89	85
AM Best, B++ Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	614	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	255	261
Reinsurance Recoverable, Allowance for Credit Loss	(2)	(2)	(2)	(2)
Net Reinsurance Recoverables	253	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 | Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(2)	(2)	(2)	(2)
Corporate | Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	0	0	0	0
Corporate | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	255	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	252	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	6,526	6,557
Reinsurance Recoverable, Allowance for Credit Loss	(102)	(102)	(96)	(96)
Net Reinsurance Recoverables	6,424	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	217	218
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Captives [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	307	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	275	279
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(44)	(42)	(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	(58)	(60)	(56)	(54)
Property, Liability and Casualty Insurance Product Line | Operating Segments [Member] | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	5,727	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	2,166	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	2,031	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	816	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	83	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	611	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	254	251
Reinsurance Recoverable, Allowance for Credit Loss	(1)	(1)	(1)	(1)
Net Reinsurance Recoverables	253	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] | Reinsurance Contract [Axis]: Before Uncollectible Reinsurance [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	(1)	(1)	(1)	(1)
Group Benefits | Operating Segments [Member] | Reinsurance Contract [Axis]: Disputes [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverable, Allowance for Credit Loss	0	0	$ 0	$ 0
Group Benefits | Operating Segments [Member] | AMBestRated [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	248	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	241	239
Group Benefits | Operating Segments [Member] | AM Best, A Rating [Member]
Reinsurance Recoverable, Credit Quality Indicator [Line Items]
Reinsurance Recoverables, Gross	1	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