Investments - Gross Unrealized Appreciation (Depreciation) on Debt Securities by Type of Issuer (Details) - USD ($) $ in Millions	Jun. 30, 2026	Dec. 31, 2025
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	$ 8,743	$ 8,660
Allowance for Credit Loss	(51)	(137)
Unrealized Appreciation	159	206
Unrealized Depreciation	(401)	(367)
Fair Value	8,450	8,362
Federal government and agency
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	217	215
Allowance for Credit Loss	0	0
Unrealized Appreciation	12	15
Unrealized Depreciation	(4)	(3)
Fair Value	225	227
State and local government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	24	24
Allowance for Credit Loss	0	0
Unrealized Appreciation	1	1
Unrealized Depreciation	0	0
Fair Value	25	25
Foreign government
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	461	450
Allowance for Credit Loss	0	0
Unrealized Appreciation	9	12
Unrealized Depreciation	(6)	(6)
Fair Value	464	456
Corporate
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	7,794	7,704
Allowance for Credit Loss	(51)	(137)
Unrealized Appreciation	135	175
Unrealized Depreciation	(369)	(332)
Fair Value	7,509	7,410
Mortgage and other asset-backed
Debt Securities, Available-for-sale [Line Items]
Amortized Cost	247	267
Allowance for Credit Loss	0	0
Unrealized Appreciation	2	3
Unrealized Depreciation	(22)	(26)
Fair Value	$ 227	$ 244

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of allowance for credit loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amortized cost excluding accrued interest, before allowance for credit loss, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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Amount excluding accrued interest, of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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