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Investments (Details) - Investment Information, Debt Securities - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2025	Jun. 30, 2024	Mar. 31, 2025	Dec. 31, 2024	Mar. 31, 2024	Dec. 31, 2023
Investment disclosure details
Fixed maturities, amortized cost	$ 91,406			$ 88,277
Allowance for expected credit losses	4			2
Gross unrealized gains	520			223
Gross unrealized losses	4,353			4,832
Fixed maturities, at fair value	87,569			83,666
Proceeds from sales of fixed maturities classified as available for sale	601	$ 1,250
Gross realized gains	3	2
Gross realized losses on sales of fixed maturities	26	41
Realized losses resulting from the early redemption of fixed maturities by the issuer prior to the bonds' maturity date	23	33
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	3,938			5,735
Allowance for expected credit losses	0			0
Gross unrealized gains	4			4
Gross unrealized losses	99			169
Fixed maturities, at fair value	3,843			5,570
Obligations of U.S. states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	31,281			29,526
Allowance for expected credit losses	0			0
Gross unrealized gains	40			43
Gross unrealized losses	2,761			2,384
Fixed maturities, at fair value	28,560			27,185
Obligations of U.S. states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	20,225			18,604
Allowance for expected credit losses	0			0
Gross unrealized gains	22			23
Gross unrealized losses	1,835			1,604
Fixed maturities, at fair value	18,412			17,023
Obligations of U.S. states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	9,476			9,268
Allowance for expected credit losses	0			0
Gross unrealized gains	14			16
Gross unrealized losses	847			704
Fixed maturities, at fair value	8,643			8,580
Obligations of U.S. states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,005			1,081
Allowance for expected credit losses	0			0
Gross unrealized gains	2			2
Gross unrealized losses	77			73
Fixed maturities, at fair value	930			1,010
Obligations of U.S. states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	575			573
Allowance for expected credit losses	0			0
Gross unrealized gains	2			2
Gross unrealized losses	2			3
Fixed maturities, at fair value	575			572
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	978			917
Allowance for expected credit losses	0			0
Gross unrealized gains	8			5
Gross unrealized losses	8			13
Fixed maturities, at fair value	978			909
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	13,182			12,888
Allowance for expected credit losses	0			0
Gross unrealized gains	137			53
Gross unrealized losses	207			336
Fixed maturities, at fair value	13,112			12,605
Corporate and all other bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	42,027			39,211
Allowance for expected credit losses	4	$ 1	$ 4	2	$ 3	$ 5
Gross unrealized gains	331			118
Gross unrealized losses	1,278			1,930
Fixed maturities, at fair value	$ 41,076			$ 37,397