Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2025	Dec. 31, 2024
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	$ 44,116	$ 41,827
Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	25,461	24,944
States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,376	6,804
Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,853	8,416
Fair Value, Recurring
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	43,636	41,061
Fixed maturities trading	480	766
Total fixed maturities	44,116	41,827
Equity securities	1,295	1,064
Short-term and other	5,222	4,453
Receivables	1	5
Payable to brokers	(34)	(88)
Fair Value, Recurring | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	26,407	25,841
Fair Value, Recurring | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,376	6,804
Fair Value, Recurring | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,853	8,416
Fair Value, Recurring | Level 1
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	227	223
Fixed maturities trading	415	766
Total fixed maturities	642	989
Equity securities	792	603
Short-term and other	5,170	4,383
Receivables
Payable to brokers	(34)	(88)
Fair Value, Recurring | Level 1 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	227	223
Fair Value, Recurring | Level 1 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale
Fair Value, Recurring | Level 1 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale
Fair Value, Recurring | Level 2
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	41,006	38,642
Fixed maturities trading	65
Total fixed maturities	41,071	38,642
Equity securities	493	441
Short-term and other	52	70
Receivables	1	5
Payable to brokers
Fair Value, Recurring | Level 2 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	24,780	24,340
Fair Value, Recurring | Level 2 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,332	6,762
Fair Value, Recurring | Level 2 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	7,894	7,540
Fair Value, Recurring | Level 3
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	2,403	2,196
Fixed maturities trading
Total fixed maturities	2,403	2,196
Equity securities	10	20
Short-term and other
Receivables
Payable to brokers
Fair Value, Recurring | Level 3 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	1,400	1,278
Fair Value, Recurring | Level 3 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	44	42
Fair Value, Recurring | Level 3 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	$ 959	$ 876