Fair Value Measurements (Details) - Fair Value Hierarchy - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2023	Mar. 31, 2023	Sep. 30, 2023	Dec. 31, 2022
Common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Transfers out of Level 3	$ 151	$ 182
Recurring basis [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			$ 73,173	$ 71,983
Other liabilities measured on a recurring basis				2
Recurring basis [Member] | Fixed maturities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			72,584	71,160
Recurring basis [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,212	5,438
Recurring basis [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			26,238	31,379
Recurring basis [Member] | Debt securities issued by foreign governments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			982	994
Recurring basis [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,523	1,991
Recurring basis [Member] | Corporate and all other bonds [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			32,629	31,358
Recurring basis [Member] | Equity securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			573	807
Recurring basis [Member] | Common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			527	763
Recurring basis [Member] | Non-redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			46	44
Recurring basis [Member] | Other Investments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			16	16
Recurring basis [Member] | Level 1 [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,762	5,886
Other liabilities measured on a recurring basis				0
Recurring basis [Member] | Level 1 [Member] | Fixed maturities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,212	5,438
Recurring basis [Member] | Level 1 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,212	5,438
Recurring basis [Member] | Level 1 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 1 [Member] | Debt securities issued by foreign governments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 1 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 1 [Member] | Corporate and all other bonds [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 1 [Member] | Equity securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			534	433
Recurring basis [Member] | Level 1 [Member] | Common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			520	418
Recurring basis [Member] | Level 1 [Member] | Non-redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			14	15
Recurring basis [Member] | Level 1 [Member] | Other Investments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			16	15
Recurring basis [Member] | Level 2 [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			66,123	65,422
Other liabilities measured on a recurring basis				0
Recurring basis [Member] | Level 2 [Member] | Fixed maturities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			66,120	65,419
Recurring basis [Member] | Level 2 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 2 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			26,238	31,379
Recurring basis [Member] | Level 2 [Member] | Debt securities issued by foreign governments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			982	994
Recurring basis [Member] | Level 2 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			6,523	1,991
Recurring basis [Member] | Level 2 [Member] | Corporate and all other bonds [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			32,377	31,055
Recurring basis [Member] | Level 2 [Member] | Equity securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			3	3
Recurring basis [Member] | Level 2 [Member] | Common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 2 [Member] | Non-redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			3	3
Recurring basis [Member] | Level 2 [Member] | Other Investments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 3 [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			288	675
Other liabilities measured on a recurring basis				2
Recurring basis [Member] | Level 3 [Member] | Fixed maturities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			252	303
Recurring basis [Member] | Level 3 [Member] | U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 3 [Member] | Obligations of U.S. states, municipalities and political subdivisions [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 3 [Member] | Debt securities issued by foreign governments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 3 [Member] | Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			0	0
Recurring basis [Member] | Level 3 [Member] | Corporate and all other bonds [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			252	303
Recurring basis [Member] | Level 3 [Member] | Equity securities [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			36	371
Recurring basis [Member] | Level 3 [Member] | Common stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			7	345
Recurring basis [Member] | Level 3 [Member] | Non-redeemable preferred stock [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			29	26
Recurring basis [Member] | Level 3 [Member] | Investment in non-public common and preferred equity securities where the fair value estimate is determined either internally or by an external fund manager [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			36	371
Recurring basis [Member] | Level 3 [Member] | Other Investments [Member]
Level within the fair value hierarchy at which the Company's financial assets and financial liabilities are measured
Total invested assets measured on a recurring basis			$ 0	$ 1