Fair Value Measurements - Assets and liabilities measured and carried at fair value in the financial statements (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Assets:
Available for sale (AFS) fixed maturities	$ 10,371	$ 10,377
Trading fixed maturities	57	57
Equity securities	1,040	1,018
Assets of managed investment entities	4,669	4,484
Other assets	80	87
Total assets accounted for at fair value	16,140	15,942
Liabilities:
Liabilities of managed investment entities	4,468	4,307
Derivative liability	28	22
Total liabilities accounted for at fair value	4,498	4,331
Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	2	2
Other liabilities — derivatives
Liabilities:
Derivative liability	28	22
Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	10,371	10,377
Trading fixed maturities	57	57
U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	199	236
States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	910	984
Foreign government
Assets:
Available for sale (AFS) fixed maturities	235	230
Residential MBS
Assets:
Available for sale (AFS) fixed maturities	1,674	1,658
Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	72	74
Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	1,593	1,687
Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	2,374	2,362
Corporate and other
Assets:
Available for sale (AFS) fixed maturities	3,314	3,146
Equity securities
Assets:
Equity securities	1,040	1,018
Other assets
Assets:
Other assets	3	6
Level 1
Assets:
Assets of managed investment entities	430	335
Total assets accounted for at fair value	1,100	1,079
Liabilities:
Liabilities of managed investment entities	411	322
Total liabilities accounted for at fair value	411	322
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 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	209	244
Trading fixed maturities	0	0
Level 1 | U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	198	235
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	11	9
Level 1 | Equity securities
Assets:
Equity securities	461	500
Level 1 | Other assets
Assets:
Other assets	0	0
Level 2
Assets:
Assets of managed investment entities	4,229	4,140
Total assets accounted for at fair value	13,743	13,633
Liabilities:
Liabilities of managed investment entities	4,047	3,976
Total liabilities accounted for at fair value	4,075	3,998
Level 2 | Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	0	0
Level 2 | Other liabilities — derivatives
Liabilities:
Derivative liability	28	22
Level 2 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	9,420	9,397
Trading fixed maturities	57	57
Level 2 | U.S. government and government agencies
Assets:
Available for sale (AFS) fixed maturities	1	1
Level 2 | States, municipalities and political subdivisions
Assets:
Available for sale (AFS) fixed maturities	908	982
Level 2 | Foreign government
Assets:
Available for sale (AFS) fixed maturities	235	230
Level 2 | Residential MBS
Assets:
Available for sale (AFS) fixed maturities	1,672	1,656
Level 2 | Commercial MBS
Assets:
Available for sale (AFS) fixed maturities	72	74
Level 2 | Collateralized loan obligations
Assets:
Available for sale (AFS) fixed maturities	1,592	1,686
Level 2 | Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	2,039	2,011
Level 2 | Corporate and other
Assets:
Available for sale (AFS) fixed maturities	2,901	2,757
Level 2 | Equity securities
Assets:
Equity securities	34	33
Level 2 | Other assets
Assets:
Other assets	3	6
Level 3
Assets:
Assets of managed investment entities	10	9
Total assets accounted for at fair value	1,297	1,230
Liabilities:
Liabilities of managed investment entities	10	9
Total liabilities accounted for at fair value	12	11
Level 3 | Contingent consideration — acquisitions
Liabilities:
Fair value of potential contingent consideration	2	2
Level 3 | Other liabilities — derivatives
Liabilities:
Derivative liability	0	0
Level 3 | Fixed maturities:
Assets:
Available for sale (AFS) fixed maturities	742	736
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	2
Level 3 | Foreign government
Assets:
Available for sale (AFS) fixed maturities	0	0
Level 3 | Residential MBS
Assets:
Available for sale (AFS) fixed maturities	2	2
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	1
Level 3 | Other asset-backed securities
Assets:
Available for sale (AFS) fixed maturities	335	351
Level 3 | Corporate and other
Assets:
Available for sale (AFS) fixed maturities	402	380
Level 3 | Equity securities
Assets:
Equity securities	545	485
Level 3 | Other assets
Assets:
Other assets	$ 0	$ 0