Investments (Details) - Investment Information, Debt Securities - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2024	Mar. 31, 2023	Dec. 31, 2023	Dec. 31, 2022
Investment disclosure details
Fixed maturities, amortized cost	$ 82,712		$ 81,781
Allowance for expected credit losses	3		5
Gross unrealized gains	246		471
Gross unrealized losses	4,964		4,440
Fixed maturities, at fair value	77,991		77,807
Proceeds from sales of fixed maturities classified as available for sale	942	$ 2,364
Gross realized gains	2	17
Gross realized losses	39	27
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	6,489		6,591
Allowance for expected credit losses	0		0
Gross unrealized gains	1		8
Gross unrealized losses	250		231
Fixed maturities, at fair value	6,240		6,368
Obligations of U.S. states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	29,665		30,294
Allowance for expected credit losses	0		0
Gross unrealized gains	73		154
Gross unrealized losses	2,226		1,942
Fixed maturities, at fair value	27,512		28,506
Obligations of U.S. states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	18,138		18,374
Allowance for expected credit losses	0		0
Gross unrealized gains	41		90
Gross unrealized losses	1,455		1,265
Fixed maturities, at fair value	16,724		17,199
Obligations of U.S. states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	9,419		9,748
Allowance for expected credit losses	0		0
Gross unrealized gains	27		52
Gross unrealized losses	700		616
Fixed maturities, at fair value	8,746		9,184
Obligations of U.S. states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,156		1,209
Allowance for expected credit losses	0		0
Gross unrealized gains	3		7
Gross unrealized losses	67		59
Fixed maturities, at fair value	1,092		1,157
Obligations of U.S. states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	952		963
Allowance for expected credit losses	0		0
Gross unrealized gains	2		5
Gross unrealized losses	4		2
Fixed maturities, at fair value	950		966
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	970		1,035
Allowance for expected credit losses	0		0
Gross unrealized gains	1		2
Gross unrealized losses	32		31
Fixed maturities, at fair value	939		1,006
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	9,076		7,874
Allowance for expected credit losses	0		0
Gross unrealized gains	68		120
Gross unrealized losses	224		176
Fixed maturities, at fair value	8,920		7,818
Corporate and all other bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	36,512		35,987
Allowance for expected credit losses	3	$ 4	5	$ 3
Gross unrealized gains	103		187
Gross unrealized losses	2,232		2,060
Fixed maturities, at fair value	$ 34,380		$ 34,109