Investments (Details) - Investment Information, Debt Securities - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Investment disclosure details
Fixed maturities, amortized cost	$ 65,630		$ 65,281
Allowance for credit losses	4		0
Gross unrealized gains	2,694		2,882
Gross unrealized losses	423		29
Fixed maturities, at fair value	67,897		68,134
Proceeds from sales of fixed maturities classified as available for sale	388	$ 769
Gross realized gains	15	21
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	2,003		2,076
Allowance for credit losses	0
Gross unrealized gains	53		19
Gross unrealized losses	1		0
Fixed maturities, at fair value	2,055		2,095
Obligations of states, municipalities and political subdivisions [Member]
Investment disclosure details
Fixed maturities, amortized cost	29,366		28,356
Allowance for credit losses	0
Gross unrealized gains	1,654		1,567
Gross unrealized losses	12		6
Fixed maturities, at fair value	31,008		29,917
Obligations of states, municipalities and political subdivisions, local general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	15,893		15,490
Allowance for credit losses	0
Gross unrealized gains	907		829
Gross unrealized losses	9		4
Fixed maturities, at fair value	16,791		16,315
Obligations of states, municipalities and political subdivisions, revenue [Member]
Investment disclosure details
Fixed maturities, amortized cost	10,158		9,731
Allowance for credit losses	0
Gross unrealized gains	593		586
Gross unrealized losses	3		2
Fixed maturities, at fair value	10,748		10,315
Obligations of states, municipalities and political subdivisions, state general obligation [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,149		1,167
Allowance for credit losses	0
Gross unrealized gains	65		64
Gross unrealized losses	0		0
Fixed maturities, at fair value	1,214		1,231
Obligations of states, municipalities and political subdivisions, pre-refunded [Member]
Investment disclosure details
Fixed maturities, amortized cost	2,166		1,968
Allowance for credit losses	0
Gross unrealized gains	89		88
Gross unrealized losses	0		0
Fixed maturities, at fair value	2,255		2,056
Debt securities issued by foreign governments [Member]
Investment disclosure details
Fixed maturities, amortized cost	1,016		1,167
Allowance for credit losses	0
Gross unrealized gains	24		8
Gross unrealized losses	0		2
Fixed maturities, at fair value	1,040		1,173
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member]
Investment disclosure details
Fixed maturities, amortized cost	3,165		3,192
Allowance for credit losses	0		0
Gross unrealized gains	147		91
Gross unrealized losses	5		3
Fixed maturities, at fair value	3,307		3,280
All other corporate bonds [Member]
Investment disclosure details
Fixed maturities, amortized cost	30,034		30,442
Allowance for credit losses	4		0
Gross unrealized gains	816		1,195
Gross unrealized losses	405		18
Fixed maturities, at fair value	30,441		31,619
Redeemable preferred stock [Member]
Investment disclosure details
Fixed maturities, amortized cost	46		48
Allowance for credit losses	0
Gross unrealized gains	0		2
Gross unrealized losses	0		0
Fixed maturities, at fair value	$ 46		$ 50

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

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