Investments (Details) - Investment Information, Losses - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	$ 16,021	$ 7,993
Continuous unrealized loss position, less than 12 months, gross unrealized losses	142	56
Continuous unrealized loss position, 12 months or longer, fair value	46,120	45,976
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	4,822	4,384
Continuous unrealized loss position, total, fair value	62,141	53,969
Continuous unrealized loss position, total, gross unrealized losses	4,964	4,440
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	309	1
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	2	5
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	9	53
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	731	667
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	1,051	726
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	2,866	1,864
Continuous unrealized loss position, less than 12 months, gross unrealized losses	17	7
Continuous unrealized loss position, 12 months or longer, fair value	2,869	2,985
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	233	224
Continuous unrealized loss position, total, fair value	5,735	4,849
Continuous unrealized loss position, total, gross unrealized losses	250	231
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	0	0
Obligations of U.S. states, municipalities and political subdivisions [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	6,958	3,868
Continuous unrealized loss position, less than 12 months, gross unrealized losses	67	31
Continuous unrealized loss position, 12 months or longer, fair value	15,198	14,351
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2,159	1,911
Continuous unrealized loss position, total, fair value	22,156	18,219
Continuous unrealized loss position, total, gross unrealized losses	2,226	1,942
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	224	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	0	2
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	8	31
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	708	642
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	940	675
Debt securities issued by foreign governments [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	134	30
Continuous unrealized loss position, less than 12 months, gross unrealized losses	1	0
Continuous unrealized loss position, 12 months or longer, fair value	696	763
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	31	31
Continuous unrealized loss position, total, fair value	830	793
Continuous unrealized loss position, total, gross unrealized losses	32	31
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	0	0
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	3,106	1,215
Continuous unrealized loss position, less than 12 months, gross unrealized losses	29	9
Continuous unrealized loss position, 12 months or longer, fair value	1,689	1,433
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	195	167
Continuous unrealized loss position, total, fair value	4,795	2,648
Continuous unrealized loss position, total, gross unrealized losses	224	176
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	44	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	0	0
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	44	0
Corporate and all other bonds [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	2,957	1,016
Continuous unrealized loss position, less than 12 months, gross unrealized losses	28	9
Continuous unrealized loss position, 12 months or longer, fair value	25,668	26,444
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2,204	2,051
Continuous unrealized loss position, total, fair value	28,625	27,460
Continuous unrealized loss position, total, gross unrealized losses	2,232	2,060
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	41	1
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost greater than 3 months, 6 months or less	2	3
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 6 months, 12 months or less	1	22
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	23	25
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	$ 67	$ 51