Income Taxes (Details) - Deferred Tax Asset and Liability - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Deferred tax assets, investments	$ 659	$ 532
Deferred tax assets, claims and claim adjustment expense reserves	708	665
Deferred tax assets, unearned premium reserves	833	772
Deferred tax assets, internally developed software	303	204
Deferred tax assets, other	261	258
Total gross deferred tax assets	2,764	2,431
Less: valuation allowance	38	35
Adjusted gross deferred tax assets	2,726	2,396
Deferred tax liabilities, deferred acquisition costs	673	627
Deferred tax liabilities, intangibles	87	70
Deferred tax liabilities, depreciation	118	125
Deferred tax liabilities, other	86	70
Total gross deferred tax liabilities	964	892
Net deferred tax asset	1,762	$ 1,504
Increase in valuation allowance	$ 3