Investments (Details) - Fixed Maturities - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Investment disclosure details
Fixed maturities, amortized cost	$ 65,281	$ 63,601
Gross unrealized gains	2,882	712
Gross unrealized losses	29	849
Fixed maturities, at fair value	68,134	63,464
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,076	2,076
Gross unrealized gains	19	4
Gross unrealized losses	0	16
Fixed maturities, at fair value	2,095	2,064
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	28,356	28,329
Gross unrealized gains	1,567	489
Gross unrealized losses	6	207
Fixed maturities, at fair value	29,917	28,611
Obligations of states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	15,490	14,473
Gross unrealized gains	829	219
Gross unrealized losses	4	120
Fixed maturities, at fair value	16,315	14,572
Obligations of states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	9,731	9,755
Gross unrealized gains	586	172
Gross unrealized losses	2	74
Fixed maturities, at fair value	10,315	9,853
Obligations of states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,167	1,329
Gross unrealized gains	64	18
Gross unrealized losses	0	13
Fixed maturities, at fair value	1,231	1,334
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,968	2,772
Gross unrealized gains	88	80
Gross unrealized losses	0	0
Fixed maturities, at fair value	2,056	2,852
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,167	1,255
Gross unrealized gains	8	7
Gross unrealized losses	2	5
Fixed maturities, at fair value	1,173	1,257
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	3,192	2,557
Gross unrealized gains	91	54
Gross unrealized losses	3	38
Fixed maturities, at fair value	3,280	2,573
All other corporate bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	30,442	29,307
Gross unrealized gains	1,195	156
Gross unrealized losses	18	583
Fixed maturities, at fair value	31,619	28,880
Redeemable preferred stock [Member]
Investment disclosure details
Fixed maturities, amortized cost	48	77
Gross unrealized gains	2	2
Gross unrealized losses	0	0
Fixed maturities, at fair value	$ 50	$ 79