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Investments (Details) - Investment Information, Debt Securities - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Jun. 30, 2025	Dec. 31, 2024	Jun. 30, 2024	Dec. 31, 2023
Investment disclosure details
Fixed maturities, amortized cost	$ 93,598			$ 88,277
Allowance for expected credit losses	4			2
Gross unrealized gains	883			223
Gross unrealized losses	3,364			4,832
Fixed maturities, at fair value	91,113			83,666
Proceeds from sales of fixed maturities classified as available for sale	779	$ 1,475
Gross realized gains	1	2
Gross realized losses on sales of fixed maturities	29	57
Realized losses resulting from the early redemption of fixed maturities by the issuer prior to the bonds' maturity date	20	34
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	4,084			5,735
Allowance for expected credit losses	0			0
Gross unrealized gains	15			4
Gross unrealized losses	86			169
Fixed maturities, at fair value	4,013			5,570
Obligations of U.S. states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	32,191			29,526
Allowance for expected credit losses	0			0
Gross unrealized gains	153			43
Gross unrealized losses	2,040			2,384
Fixed maturities, at fair value	30,304			27,185
Obligations of U.S. states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	21,171			18,604
Allowance for expected credit losses	0			0
Gross unrealized gains	103			23
Gross unrealized losses	1,342			1,604
Fixed maturities, at fair value	19,932			17,023
Obligations of U.S. states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	9,677			9,268
Allowance for expected credit losses	0			0
Gross unrealized gains	42			16
Gross unrealized losses	642			704
Fixed maturities, at fair value	9,077			8,580
Obligations of U.S. states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,019			1,081
Allowance for expected credit losses	0			0
Gross unrealized gains	5			2
Gross unrealized losses	55			73
Fixed maturities, at fair value	969			1,010
Obligations of U.S. states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	324			573
Allowance for expected credit losses	0			0
Gross unrealized gains	3			2
Gross unrealized losses	1			3
Fixed maturities, at fair value	326			572
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	984			917
Allowance for expected credit losses	0			0
Gross unrealized gains	10			5
Gross unrealized losses	6			13
Fixed maturities, at fair value	988			909
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	13,287			12,888
Allowance for expected credit losses	0			0
Gross unrealized gains	225			53
Gross unrealized losses	151			336
Fixed maturities, at fair value	13,361			12,605
Corporate and all other bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	43,052			39,211
Allowance for expected credit losses	4	$ 0	$ 4	2	$ 1	$ 5
Gross unrealized gains	480			118
Gross unrealized losses	1,081			1,930
Fixed maturities, at fair value	$ 42,447			$ 37,397