Fair Value Measurements - Assets and liabilities measured and carried at fair value in the financial statements (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Assets:
Available for sale (AFS) fixed maturities	$ 9,931	$ 10,095
Trading fixed maturities	51	32
Equity securities	1,007	1,010
Total assets	30,825	28,831
Total assets accounted for at fair value	15,860	16,584
Liabilities:
Total liabilities	26,844	24,779
Derivative liability	48	42
Total liabilities accounted for at fair value	4,778	5,399
Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	2	25
Other liabilities — derivatives
Liabilities:
Derivative liability	48	42
Variable interest entity, primary beneficiary
Assets:
Total assets	4,871	5,447
Liabilities:
Total liabilities	4,728	5,332
Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	9,931	10,095
Trading fixed maturities	51	32
U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	229	219
States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	911	1,186
Foreign government
Assets:
Available for sale (AFS) fixed maturities	218	226
Residential MBS
Assets:
Available for sale (AFS) fixed maturities	1,619	1,598
Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	76	85
Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	1,723	1,921
Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	2,277	2,245
Corporate and other
Assets:
Available for sale (AFS) fixed maturities	2,878	2,615
Equity securities
Assets:
Equity securities	1,007	1,010
Level 1
Assets:
Total assets accounted for at fair value	1,432	1,442
Liabilities:
Total liabilities accounted for at fair value	654	645
Level 1 | Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	0	0
Level 1 | Other liabilities — derivatives
Liabilities:
Derivative liability	0	0
Level 1 | Variable interest entity, primary beneficiary
Assets:
Total assets	674	659
Liabilities:
Total liabilities	654	645
Level 1 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	237	227
Trading fixed maturities	0	0
Level 1 | U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	228	219
Level 1 | States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Foreign government
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Residential MBS
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 1 | Corporate and other
Assets:
Available for sale (AFS) fixed maturities	9	8
Level 1 | Equity securities
Assets:
Equity securities	521	556
Level 2
Assets:
Total assets accounted for at fair value	13,274	14,040
Liabilities:
Total liabilities accounted for at fair value	4,112	4,718
Level 2 | Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	0	0
Level 2 | Other liabilities — derivatives
Liabilities:
Derivative liability	48	42
Level 2 | Variable interest entity, primary beneficiary
Assets:
Total assets	4,187	4,777
Liabilities:
Total liabilities	4,064	4,676
Level 2 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	9,004	9,204
Trading fixed maturities	51	32
Level 2 | U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	1	0
Level 2 | States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	909	1,181
Level 2 | Foreign government
Assets:
Available for sale (AFS) fixed maturities	218	226
Level 2 | Residential MBS
Assets:
Available for sale (AFS) fixed maturities	1,614	1,589
Level 2 | Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	76	85
Level 2 | Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	1,722	1,919
Level 2 | Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	1,947	1,916
Level 2 | Corporate and other
Assets:
Available for sale (AFS) fixed maturities	2,517	2,288
Level 2 | Equity securities
Assets:
Equity securities	32	27
Level 3
Assets:
Total assets accounted for at fair value	1,154	1,102
Liabilities:
Total liabilities accounted for at fair value	12	36
Level 3 | Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	2	25
Level 3 | Other liabilities — derivatives
Liabilities:
Derivative liability	0	0
Level 3 | Variable interest entity, primary beneficiary
Assets:
Total assets	10	11
Liabilities:
Total liabilities	10	11
Level 3 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	690	664
Trading fixed maturities	0	0
Level 3 | U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 3 | States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	2	5
Level 3 | Foreign government
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 3 | Residential MBS
Assets:
Available for sale (AFS) fixed maturities	5	9
Level 3 | Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 3 | Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	1	2
Level 3 | Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	330	329
Level 3 | Corporate and other
Assets:
Available for sale (AFS) fixed maturities	352	319
Level 3 | Equity securities
Assets:
Equity securities	$ 454	$ 427