Investments - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Dec. 31, 2017
Available-for-sale Securities Including Securities Pledged [Line Items]
Embedded Derivatives			$ 12
OTTI			13
Securities pledged, Amortized Cost	$ 938		864
Total equity securities, Amortized Cost	48		45
Total fixed maturities and equity securities, Amortized Cost			22,760
Total fixed maturities and equity securities, Gross Unrealized Capital Gains			1,510
Total fixed maturities and equity securities, Gross Unrealized Capital Losses			140
Total fixed maturities and equity securities, Fair Value			24,142
Impaired available-for-sale securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Net unrealized gains on impaired available-for-sale securities	131	$ 190
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	451		547
Fixed maturities, Gross Unrealized Capital Gains	69		109
Fixed maturities, Gross Unrealized Capital Losses	0		0
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	520		656
OTTI	0		0
U.S. government agencies and authorities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	0		3
Fixed maturities, Gross Unrealized Capital Gains	0		0
Fixed maturities, Gross Unrealized Capital Losses	0		0
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	0		3
OTTI	0		0
State, municipalities and political subdivisions
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	752		842
Fixed maturities, Gross Unrealized Capital Gains	13		40
Fixed maturities, Gross Unrealized Capital Losses	14		4
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	751		878
OTTI	0		0
U.S. corporate public securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	7,924		8,476
Fixed maturities, Gross Unrealized Capital Gains	354		786
Fixed maturities, Gross Unrealized Capital Losses	116		26
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	8,162		9,236
OTTI	0		0
U.S. corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	3,757		3,387
Fixed maturities, Gross Unrealized Capital Gains	86		148
Fixed maturities, Gross Unrealized Capital Losses	96		38
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	3,747		3,497
OTTI	0		0
Foreign corporate public securities and foreign governments
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	2,555		2,594
Fixed maturities, Gross Unrealized Capital Gains	83		192
Fixed maturities, Gross Unrealized Capital Losses	51		9
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,587		2,777
OTTI	0		0
Foreign corporate private securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	3,193		3,105
Fixed maturities, Gross Unrealized Capital Gains	52		155
Fixed maturities, Gross Unrealized Capital Losses	74		45
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	3,171		3,215
OTTI	0		7
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	2,837		2,517
Fixed maturities, Gross Unrealized Capital Gains	87		119
Fixed maturities, Gross Unrealized Capital Losses	46		19
Embedded Derivatives	8		12
Fixed maturities, including securities pledged, Fair Value	2,886		2,629
OTTI	3		4
Agency
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,930		1,878
Fixed maturities, Gross Unrealized Capital Gains	42		65
Fixed maturities, Gross Unrealized Capital Losses	38		17
Embedded Derivatives	4		6
Fixed maturities, including securities pledged, Fair Value	1,938		1,932
OTTI	0		0
Non-Agency
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	907		639
Fixed maturities, Gross Unrealized Capital Gains	45		54
Fixed maturities, Gross Unrealized Capital Losses	8		2
Embedded Derivatives	4		6
Fixed maturities, including securities pledged, Fair Value	948		697
OTTI	3		4
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,731		1,437
Fixed maturities, Gross Unrealized Capital Gains	9		39
Fixed maturities, Gross Unrealized Capital Losses	42		6
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,698		1,470
OTTI	0		0
Other asset-backed securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,141		671
Fixed maturities, Gross Unrealized Capital Gains	5		11
Fixed maturities, Gross Unrealized Capital Losses	7		1
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,139		681
OTTI	2		2
Fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	24,341		23,579
Fixed maturities, Gross Unrealized Capital Gains	758		1,599
Fixed maturities, Gross Unrealized Capital Losses	446		148
Embedded Derivatives	8		12
Fixed maturities, including securities pledged, Fair Value	24,661		25,042
OTTI	5		13
Securities pledged, Amortized Cost	938		864
Securities pledged, Gross Unrealized Capital Gains	62		104
Securities pledged, Gross Unrealized Capital Losses	15		8
Securities pledged	985		960
Total fixed maturities, less securities pledged, Amortized Cost	23,403		22,715
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	696		1,495
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	431		140
Total fixed maturities, less securities pledged, Fair Value	$ 23,676		24,082
Equity securities
Available-for-sale Securities Including Securities Pledged [Line Items]
Embedded Derivatives			0
OTTI			0
Total equity securities, Amortized Cost			45
Equity securities, Gross Unrealized Capital Gains			15
Equity securities, Gross Unrealized Capital Losses			0
Equity securities			$ 60