Investments - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged, Amortized Cost	$ 869	$ 867
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	450	651
Fixed maturities, Gross Unrealized Capital Gains	126	87
Fixed maturities, Gross Unrealized Capital Losses	0	0
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	576	738
OTTI	0	0
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	752	754
Fixed maturities, Gross Unrealized Capital Gains	62	18
Fixed maturities, Gross Unrealized Capital Losses	1	8
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	813	764
OTTI	0	0
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	7,340	7,908
Fixed maturities, Gross Unrealized Capital Gains	762	288
Fixed maturities, Gross Unrealized Capital Losses	32	181
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	8,070	8,015
OTTI	0	0
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,711	3,686
Fixed maturities, Gross Unrealized Capital Gains	244	73
Fixed maturities, Gross Unrealized Capital Losses	25	106
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	3,930	3,653
OTTI	0	0
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	2,500	2,551
Fixed maturities, Gross Unrealized Capital Gains	211	69
Fixed maturities, Gross Unrealized Capital Losses	15	80
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	2,696	2,540
OTTI	0	0
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,160	3,235
Fixed maturities, Gross Unrealized Capital Gains	156	37
Fixed maturities, Gross Unrealized Capital Losses	9	97
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	3,307	3,175
OTTI	0	0
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	3,481	2,966
Fixed maturities, Gross Unrealized Capital Gains	139	93
Fixed maturities, Gross Unrealized Capital Losses	14	32
Embedded Derivatives	11	9
Fixed maturities, including securities pledged, Fair Value	3,617	3,036
OTTI	3	3
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	2,152	1,917
Fixed maturities, Gross Unrealized Capital Gains	109	16
Fixed maturities, Gross Unrealized Capital Losses	2	28
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	2,259	1,905
OTTI	0	0
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	1,428	1,230
Fixed maturities, Gross Unrealized Capital Gains	16	6
Fixed maturities, Gross Unrealized Capital Losses	12	28
Embedded Derivatives	0	0
Fixed maturities, including securities pledged, Fair Value	1,432	1,208
OTTI	1	2
Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Amortized Cost	24,974	24,898
Fixed maturities, Gross Unrealized Capital Gains	1,825	687
Fixed maturities, Gross Unrealized Capital Losses	110	560
Embedded Derivatives	11	9
Fixed maturities, including securities pledged, Fair Value	26,700	25,034
OTTI	4	5
Total fixed maturities, less securities pledged, Amortized Cost	24,105	24,031
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	1,712	642
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	103	530
Total fixed maturities, less securities pledged, Fair Value	25,725	24,152
Impaired available-for-sale securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Net unrealized gains on impaired available-for-sale securities	187	137
Collateral Pledged
Available-for-sale Securities Including Securities Pledged [Line Items]
Securities pledged	975	882
Collateral Pledged | Embedded derivatives - fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Embedded Derivatives	0	0
Securities pledged	975	882
OTTI	0	0
Securities pledged, Amortized Cost	869	867
Securities pledged, Gross Unrealized Capital Gains	113	45
Securities pledged, Gross Unrealized Capital Losses	$ 7	$ 30