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Investments (Details) - Investment Information, Debt Securities - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020	Dec. 31, 2019
Investment disclosure details
Fixed maturities, amortized cost	$ 65,430			$ 65,281
Allowance for expected credit losses	8		$ 4	0
Gross unrealized gains	4,695			2,882
Gross unrealized losses	63			29
Fixed maturities, at fair value	70,054			68,134
Proceeds from sales of fixed maturities classified as available for sale	1,220	$ 1,495
Gross realized gains	31	35
Gross realized losses	1	$ 4
U.S. Treasury securities and obligations of U.S. government and government agencies and authorities [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,046			2,076
Allowance for expected credit losses	0
Gross unrealized gains	49			19
Gross unrealized losses	0			0
Fixed maturities, at fair value	2,095			2,095
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	29,810			28,356
Allowance for expected credit losses	0
Gross unrealized gains	2,259			1,567
Gross unrealized losses	1			6
Fixed maturities, at fair value	32,068			29,917
Obligations of states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	16,040			15,490
Allowance for expected credit losses	0
Gross unrealized gains	1,225			829
Gross unrealized losses	1			4
Fixed maturities, at fair value	17,264			16,315
Obligations of states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	10,298			9,731
Allowance for expected credit losses	0
Gross unrealized gains	818			586
Gross unrealized losses	0			2
Fixed maturities, at fair value	11,116			10,315
Obligations of states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,144			1,167
Allowance for expected credit losses	0
Gross unrealized gains	83			64
Gross unrealized losses	0			0
Fixed maturities, at fair value	1,227			1,231
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,328			1,968
Allowance for expected credit losses	0
Gross unrealized gains	133			88
Gross unrealized losses	0			0
Fixed maturities, at fair value	2,461			2,056
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,023			1,167
Allowance for expected credit losses	0
Gross unrealized gains	28			8
Gross unrealized losses	0			2
Fixed maturities, at fair value	1,051			1,173
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,910			3,192
Allowance for expected credit losses	0		0	0
Gross unrealized gains	174			91
Gross unrealized losses	0			3
Fixed maturities, at fair value	3,084			3,280
All other corporate bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	29,619			30,442
Allowance for expected credit losses	8		$ 4	0
Gross unrealized gains	2,184			1,195
Gross unrealized losses	62			18
Fixed maturities, at fair value	31,733			31,619
Redeemable preferred stock [Member]
Investment disclosure details
Fixed maturities, amortized cost	22			48
Allowance for expected credit losses	0
Gross unrealized gains	1			2
Gross unrealized losses	0			0
Fixed maturities, at fair value	$ 23			$ 50