Fair Value - Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2026	Dec. 31, 2025
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	$ 43,180	$ 43,351
Fixed maturities trading	390	633
Total fixed maturities	43,570	43,984
Equity securities	1,354	1,292
Short-term and other	5,050	5,871
Payable to brokers	(37)	(43)
Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	26,000	26,250
States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,572	8,431
Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,608	8,670
Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	43,180	43,351
Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities trading	390	633
Level 1
Assets and Liabilities Measured at Fair Value [Abstract]
Total fixed maturities	636	841
Equity securities	818	762
Short-term and other	5,019	5,820
Payable to brokers	(37)	(43)
Level 1 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	246	238
Level 1 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale
Level 1 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale
Level 1 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	246	238
Level 1 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities trading	390	603
Level 2
Assets and Liabilities Measured at Fair Value [Abstract]
Total fixed maturities	40,421	40,617
Equity securities	504	497
Short-term and other	31	51
Payable to brokers
Level 2 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	24,240	24,529
Level 2 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	8,528	8,386
Level 2 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	7,653	7,672
Level 2 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	40,421	40,587
Level 2 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities trading		30
Level 3
Assets and Liabilities Measured at Fair Value [Abstract]
Total fixed maturities	2,513	2,526
Equity securities	32	33
Short-term and other
Payable to brokers
Level 3 | Corporate bonds and other
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	1,514	1,483
Level 3 | States, municipalities and political subdivisions
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	44	45
Level 3 | Asset-backed
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	955	998
Level 3 | Fixed maturities available-for-sale
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities available-for-sale	2,513	2,526
Level 3 | Fixed maturities trading
Assets and Liabilities Measured at Fair Value [Abstract]
Fixed maturities trading