Investments (excluding Consolidated Investment Entities) - 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]
Fixed maturities, including securities pledged, Amortized Cost	$ 44,386		$ 44,366
Embedded Derivatives			37
Fixed maturities, including securities pledged, Fair Value	46,104		48,329
Securities pledged, Amortized Cost	1,882		1,823
Securities pledged	1,994		2,087
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities			29
Total equity securities, Amortized Cost	320		353
Equity securities, at fair value	385		380
Total fixed maturities and equity securities, Amortized Cost			47,737
Total fixed maturities and equity securities, Gross Unrealized Capital Gains			4,176
Total fixed maturities and equity securities, Gross Unrealized Losses			223
Total fixed maturities and equity securities, Fair Value			51,727
U.S. Treasuries
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,815		2,047
Fixed maturities, Gross Unrealized Capital Gains	365		477
Fixed maturities, Gross Unrealized Capital Losses	4		2
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,176		2,522
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	204		223
Fixed maturities, Gross Unrealized Capital Gains	39		52
Fixed maturities, Gross Unrealized Capital Losses	0		0
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	243		275
OTTI	0	0
State, municipalities and political subdivisions
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,648		1,856
Fixed maturities, Gross Unrealized Capital Gains	32		68
Fixed maturities, Gross Unrealized Capital Losses	21		11
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,659		1,913
OTTI	0	0
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	19,541		20,857
Fixed maturities, Gross Unrealized Capital Gains	1,297		2,451
Fixed maturities, Gross Unrealized Capital Losses	261		50
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	20,577		23,258
OTTI	0
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities			0
U.S. corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	6,224		5,628
Fixed maturities, Gross Unrealized Capital Gains	178		255
Fixed maturities, Gross Unrealized Capital Losses	141		50
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	6,261		5,833
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	5,259		5,241
Fixed maturities, Gross Unrealized Capital Gains	252		493
Fixed maturities, Gross Unrealized Capital Losses	111		18
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	5,400		5,716
OTTI	0	0
Foreign corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	5,247		4,974
Fixed maturities, Gross Unrealized Capital Gains	110		251
Fixed maturities, Gross Unrealized Capital Losses	105		64
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	5,252		5,161
OTTI		10
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	0
Residential mortgage-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	4,496		4,247
Fixed maturities, Gross Unrealized Capital Gains	237		274
Fixed maturities, Gross Unrealized Capital Losses	66		34
Embedded Derivatives	25		37
Fixed maturities, including securities pledged, Fair Value	4,692		4,524
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	13		16
Residential mortgage-backed securities, Agency
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	2,957		2,990
Fixed maturities, Gross Unrealized Capital Gains	141		164
Fixed maturities, Gross Unrealized Capital Losses	56		30
Embedded Derivatives	14		21
Fixed maturities, including securities pledged, Fair Value	3,056		3,145
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	0		0
Residential mortgage-backed securities, Non-Agency
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,539		1,257
Fixed maturities, Gross Unrealized Capital Gains	96		110
Fixed maturities, Gross Unrealized Capital Losses	10		4
Embedded Derivatives	11		16
Fixed maturities, including securities pledged, Fair Value	1,636		1,379
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	13		16
Commercial mortgage-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	2,954		2,646
Fixed maturities, Gross Unrealized Capital Gains	27		69
Fixed maturities, Gross Unrealized Capital Losses	49		11
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,932		2,704
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	0		0
Other asset-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,863		1,488
Fixed maturities, Gross Unrealized Capital Gains	35		43
Fixed maturities, Gross Unrealized Capital Losses	9		3
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,889		1,528
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	3		3
Fixed maturities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	49,251		49,207
Fixed maturities, Gross Unrealized Capital Gains	2,572		4,433
Fixed maturities, Gross Unrealized Capital Losses	767		243
Embedded Derivatives	25		37
Fixed maturities, including securities pledged, Fair Value	51,081		53,434
Securities pledged, Amortized Cost	1,882		1,823
Securities pledged, Gross Unrealized Capital Gains	151		284
Securities pledged, Gross Unrealized Capital Losses	39		20
Securities pledged	1,994		2,087
Total fixed maturities, less securities pledged, Amortized Cost	47,369		47,384
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	2,421		4,149
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	728		223
Total fixed maturities, less securities pledged, Fair Value	49,087		51,347
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	16		29
Common Stock
Available-for-sale Securities, Including Securities Pledged [Line Items]
Embedded Derivatives			0
OTTI		0
Total equity securities, Amortized Cost			272
Equity securities, Gross Unrealized Capital Gains			1
Equity securities, Gross Unrealized Capital Losses			0
Equity securities, at fair value			273
Preferred stock
Available-for-sale Securities, Including Securities Pledged [Line Items]
Embedded Derivatives			0
OTTI		0
Total equity securities, Amortized Cost			81
Equity securities, Gross Unrealized Capital Gains			26
Equity securities, Gross Unrealized Capital Losses			0
Equity securities, at fair value			107
Equity securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Embedded Derivatives			0
OTTI		0
Total equity securities, Amortized Cost			353
Equity securities, Gross Unrealized Capital Gains			27
Equity securities, Gross Unrealized Capital Losses			0
Equity securities, at fair value			$ 380
Impaired available-for-sale securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net unrealized gains on impaired available-for-sale securities	$ 335	$ 441