Income Taxes - Schedule of Components of the Deferred Income Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2025	Dec. 31, 2024
Components of Deferred Tax Assets [Abstract]
Unearned premium reserves	$ 1,046	$ 978
Discount on loss reserves	312	292
Net operating loss carryover	222	232
Accrued compensation	142	131
Research & development capitalization	116	317
Other postretirement benefits	6	7
Pension	1	8
Unrealized net capital losses	0	209
Other	145	185
Total deferred tax assets before valuation allowance	1,990	2,359
Valuation allowance	(68)	(69)
Total deferred tax assets after valuation allowance	1,922	2,290
Deferred Tax Liabilities, Gross [Abstract]
DAC	(1,272)	(1,173)
Investments	(439)	(479)
Depreciable assets	(103)	(123)
Unrealized net capital gains	(85)	0
Intangible assets	(44)	(66)
Other	(206)	(218)
Total deferred tax liabilities	(2,149)	(2,059)
Net deferred tax (liabilities) assets	$ (227)	0
Net deferred tax (liabilities) assets		$ 231