Investments (Details) - Investment Information, Losses - USD ($) $ in Millions	Jun. 30, 2024	Dec. 31, 2023
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	$ 17,477	$ 7,993
Continuous unrealized loss position, less than 12 months, gross unrealized losses	189	56
Continuous unrealized loss position, 12 months or longer, fair value	48,315	45,976
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	5,034	4,384
Continuous unrealized loss position, total, fair value	65,792	53,969
Continuous unrealized loss position, total, gross unrealized losses	5,223	4,440
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	170	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	307	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	3	53
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	762	667
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	1,242	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	1,695	1,864
Continuous unrealized loss position, less than 12 months, gross unrealized losses	8	7
Continuous unrealized loss position, 12 months or longer, fair value	4,048	2,985
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	235	224
Continuous unrealized loss position, total, fair value	5,743	4,849
Continuous unrealized loss position, total, gross unrealized losses	243	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	7,190	3,868
Continuous unrealized loss position, less than 12 months, gross unrealized losses	92	31
Continuous unrealized loss position, 12 months or longer, fair value	16,298	14,351
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2,345	1,911
Continuous unrealized loss position, total, fair value	23,488	18,219
Continuous unrealized loss position, total, gross unrealized losses	2,437	1,942
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	139	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	234	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	0	31
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	744	642
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	1,117	675
Debt securities issued by foreign governments [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	193	30
Continuous unrealized loss position, less than 12 months, gross unrealized losses	1	0
Continuous unrealized loss position, 12 months or longer, fair value	590	763
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	26	31
Continuous unrealized loss position, total, fair value	783	793
Continuous unrealized loss position, total, gross unrealized losses	27	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	4,009	1,215
Continuous unrealized loss position, less than 12 months, gross unrealized losses	43	9
Continuous unrealized loss position, 12 months or longer, fair value	2,332	1,433
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	219	167
Continuous unrealized loss position, total, fair value	6,341	2,648
Continuous unrealized loss position, total, gross unrealized losses	262	176
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	18	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	44	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	62	0
Corporate and all other bonds [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	4,390	1,016
Continuous unrealized loss position, less than 12 months, gross unrealized losses	45	9
Continuous unrealized loss position, 12 months or longer, fair value	25,047	26,444
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2,209	2,051
Continuous unrealized loss position, total, fair value	29,437	27,460
Continuous unrealized loss position, total, gross unrealized losses	2,254	2,060
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, 3 months or less	13	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	29	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	3	22
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, greater than 12 months	18	25
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	$ 63	$ 51