Investments - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Mar. 31, 2020
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged, amortized costs	$ 749	$ 848
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	565	566
Fixed maturities, Gross Unrealized Capital Gains	129	233
Fixed maturities, Gross Unrealized Capital Losses	3	0
Embedded Derivatives	0	0
Fair Value	691	799
OTTI	0	0
US Treasury and Government
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	19	19
Fixed maturities, Gross Unrealized Capital Gains	0	1
Fixed maturities, Gross Unrealized Capital Losses	0	0
Embedded Derivatives	0	0
Fair Value	19	20
OTTI	0	0
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	747	742
Fixed maturities, Gross Unrealized Capital Gains	68	68
Fixed maturities, Gross Unrealized Capital Losses	0	2
Embedded Derivatives	0	0
Fair Value	815	808
OTTI	0	0
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	7,103	7,011
Fixed maturities, Gross Unrealized Capital Gains	941	696
Fixed maturities, Gross Unrealized Capital Losses	13	200
Embedded Derivatives	0	0
Fair Value	8,031	7,507
OTTI	0	0
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,776	3,754
Fixed maturities, Gross Unrealized Capital Gains	306	154
Fixed maturities, Gross Unrealized Capital Losses	16	97
Embedded Derivatives	0	0
Fair Value	4,066	3,811
OTTI	0	0
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	2,417	2,423
Fixed maturities, Gross Unrealized Capital Gains	265	147
Fixed maturities, Gross Unrealized Capital Losses	3	73
Embedded Derivatives	0	0
Fair Value	2,679	2,497
OTTI	0	0
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,171	3,153
Fixed maturities, Gross Unrealized Capital Gains	205	54
Fixed maturities, Gross Unrealized Capital Losses	1	138
Embedded Derivatives	0	0
Fair Value	3,375	3,068
OTTI	0	1
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,685	4,138
Fixed maturities, Gross Unrealized Capital Gains	125	147
Fixed maturities, Gross Unrealized Capital Losses	11	131
Embedded Derivatives	11	15
Fair Value	3,810	4,169
OTTI	2	0
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	2,381	2,553
Fixed maturities, Gross Unrealized Capital Gains	122	132
Fixed maturities, Gross Unrealized Capital Losses	3	231
Embedded Derivatives	0	0
Fair Value	2,500	2,453
OTTI	0	1
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	1,472	1,478
Fixed maturities, Gross Unrealized Capital Gains	15	6
Fixed maturities, Gross Unrealized Capital Losses	13	142
Embedded Derivatives	0	0
Fair Value	1,474	1,340
OTTI	1	2
Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	25,336	25,837
Fixed maturities, Gross Unrealized Capital Gains	2,176	1,638
Fixed maturities, Gross Unrealized Capital Losses	63	1,014
Embedded Derivatives	11	15
Fair Value	27,460	26,472
OTTI	3	4
Total fixed maturities, less securities pledged, Amortized Cost	24,587	24,989
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	2,091	1,535
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	57	982
Total fixed maturities, less securities pledged, Fair Value	26,632	25,553
Impaired available-for-sale securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Net unrealized gains on impaired available-for-sale securities	137
Collateral Pledged
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged	828	919
Collateral Pledged | Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Embedded Derivatives	0	0
OTTI	0	0
Securities pledged, amortized costs	749	848
Securities pledged, Gross Unrealized Capital Gains	85	103
Securities pledged, Gross Unrealized Capital Losses	6	32
Securities pledged	$ 828	$ 919