Investments (Details) - Investment Information, Losses - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	$ 6,495	$ 1,045
Continuous unrealized loss position, less than 12 months, gross unrealized losses	117	8
Continuous unrealized loss position, 12 months or longer, fair value	65	98
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2	3
Continuous unrealized loss position, total, fair value	6,560	1,143
Continuous unrealized loss position, total, gross unrealized losses	119	11
Unrealized investment losses on fixed maturity investments for which fair value is less than 80% of amortized cost, total	0
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	451	92
Continuous unrealized loss position, less than 12 months, gross unrealized losses	8	0
Continuous unrealized loss position, 12 months or longer, fair value	0	0
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	0	0
Continuous unrealized loss position, total, fair value	451	92
Continuous unrealized loss position, total, gross unrealized losses	8	0
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	2,719	245
Continuous unrealized loss position, less than 12 months, gross unrealized losses	37	2
Continuous unrealized loss position, 12 months or longer, fair value	0	0
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	0	0
Continuous unrealized loss position, total, fair value	2,719	245
Continuous unrealized loss position, total, gross unrealized losses	37	2
Debt securities issued by foreign governments [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	273	7
Continuous unrealized loss position, less than 12 months, gross unrealized losses	3	0
Continuous unrealized loss position, 12 months or longer, fair value	0	0
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	0	0
Continuous unrealized loss position, total, fair value	273	7
Continuous unrealized loss position, total, gross unrealized losses	3	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	45	20
Continuous unrealized loss position, less than 12 months, gross unrealized losses	1	0
Continuous unrealized loss position, 12 months or longer, fair value	1	1
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	0	0
Continuous unrealized loss position, total, fair value	46	21
Continuous unrealized loss position, total, gross unrealized losses	1	0
All other corporate bonds [Member]
Investment disclosure details
Continuous unrealized loss position, less than 12 months, fair value	3,007	681
Continuous unrealized loss position, less than 12 months, gross unrealized losses	68	6
Continuous unrealized loss position, 12 months or longer, fair value	64	97
Continuous unrealized loss position, 12 months or longer, gross unrealized losses	2	3
Continuous unrealized loss position, total, fair value	3,071	778
Continuous unrealized loss position, total, gross unrealized losses	$ 70	$ 9