Investments - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Available-for-sale Securities Including Securities Pledged [Line Items]
Embedded Derivatives			$ 12
OTTI			13
Securities pledged, Amortized Cost	$ 853		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	148	$ 190
U.S. Treasuries
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	464		547
Fixed maturities, Gross Unrealized Capital Gains	84		109
Fixed maturities, Gross Unrealized Capital Losses	1		0
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	547		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	751		842
Fixed maturities, Gross Unrealized Capital Gains	20		40
Fixed maturities, Gross Unrealized Capital Losses	8		4
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	763		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	7,968		8,476
Fixed maturities, Gross Unrealized Capital Gains	369		786
Fixed maturities, Gross Unrealized Capital Losses	119		26
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	8,218		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	3,684		3,387
Fixed maturities, Gross Unrealized Capital Gains	95		148
Fixed maturities, Gross Unrealized Capital Losses	90		38
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	3,689		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	2,481		2,594
Fixed maturities, Gross Unrealized Capital Gains	90		192
Fixed maturities, Gross Unrealized Capital Losses	53		9
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,518		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	3,274		3,105
Fixed maturities, Gross Unrealized Capital Gains	62		155
Fixed maturities, Gross Unrealized Capital Losses	65		45
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	3,271		3,215
OTTI	0		7
Residential mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	2,881		2,517
Fixed maturities, Gross Unrealized Capital Gains	94		119
Fixed maturities, Gross Unrealized Capital Losses	38		19
Embedded Derivatives	9		12
Fixed maturities, including securities pledged, Fair Value	2,946		2,629
OTTI	4		4
Agency
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,998		1,878
Fixed maturities, Gross Unrealized Capital Gains	48		65
Fixed maturities, Gross Unrealized Capital Losses	32		17
Embedded Derivatives	4		6
Fixed maturities, including securities pledged, Fair Value	2,018		1,932
OTTI	0		0
Non-Agency
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	883		639
Fixed maturities, Gross Unrealized Capital Gains	46		54
Fixed maturities, Gross Unrealized Capital Losses	6		2
Embedded Derivatives	5		6
Fixed maturities, including securities pledged, Fair Value	928		697
OTTI	4		4
Commercial mortgage-backed
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,627		1,437
Fixed maturities, Gross Unrealized Capital Gains	13		39
Fixed maturities, Gross Unrealized Capital Losses	27		6
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,613		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	1,084		671
Fixed maturities, Gross Unrealized Capital Gains	6		11
Fixed maturities, Gross Unrealized Capital Losses	5		1
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,085		681
OTTI	2		2
Fixed maturities
Available-for-sale Securities Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	24,214		23,579
Fixed maturities, Gross Unrealized Capital Gains	833		1,599
Fixed maturities, Gross Unrealized Capital Losses	406		148
Embedded Derivatives	9		12
Fixed maturities, including securities pledged, Fair Value	24,650		25,042
OTTI	6		13
Securities pledged, Amortized Cost	853		864
Securities pledged, Gross Unrealized Capital Gains	70		104
Securities pledged, Gross Unrealized Capital Losses	16		8
Securities pledged	907		960
Total fixed maturities, less securities pledged, Amortized Cost	23,361		22,715
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	763		1,495
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	390		140
Total fixed maturities, less securities pledged, Fair Value	$ 23,743		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