Investments (excluding Consolidated Investment Entities) - Fixed Maturities and Equity Securities (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	$ 44,806		$ 45,241
Fixed maturities, including securities pledged, Fair Value	49,150		46,298
Securities pledged, Amortized Cost	1,739		1,824
Total equity securities, Amortized Cost	335		255
U.S. Treasuries
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,666		1,937
Fixed maturities, Gross Unrealized Capital Gains	500		360
Fixed maturities, Gross Unrealized Capital Losses	0		2
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,166		2,295
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	197		204
Fixed maturities, Gross Unrealized Capital Gains	52		38
Fixed maturities, Gross Unrealized Capital Losses	0		0
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	249		242
OTTI	0		0
State, municipalities and political subdivisions
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	1,642		1,652
Fixed maturities, Gross Unrealized Capital Gains	114		29
Fixed maturities, Gross Unrealized Capital Losses	2		22
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	1,754		1,659
OTTI	0		0
U.S. corporate public securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	18,170		19,210
Fixed maturities, Gross Unrealized Capital Gains	2,307		1,053
Fixed maturities, Gross Unrealized Capital Losses	67		415
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	20,410		19,848
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	6,292		6,264
Fixed maturities, Gross Unrealized Capital Gains	444		138
Fixed maturities, Gross Unrealized Capital Losses	38		170
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	6,698		6,232
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	5,320		5,429
Fixed maturities, Gross Unrealized Capital Gains	521		193
Fixed maturities, Gross Unrealized Capital Losses	31		167
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	5,810		5,455
OTTI	0		0
Foreign corporate private securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	5,027		5,176
Fixed maturities, Gross Unrealized Capital Gains	250		70
Fixed maturities, Gross Unrealized Capital Losses	15		152
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	5,262		5,094
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	0		0
Residential mortgage-backed
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	5,282		4,616
Fixed maturities, Gross Unrealized Capital Gains	285		214
Fixed maturities, Gross Unrealized Capital Losses	20		53
Embedded Derivatives	29		26
Fixed maturities, including securities pledged, Fair Value	5,576		4,803
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	10		11
Commercial mortgage-backed securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	3,892		3,438
Fixed maturities, Gross Unrealized Capital Gains	203		33
Fixed maturities, Gross Unrealized Capital Losses	5		55
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	4,090		3,416
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	2,415		2,095
Fixed maturities, Gross Unrealized Capital Gains	46		30
Fixed maturities, Gross Unrealized Capital Losses	23		48
Embedded Derivatives	0		0
Fixed maturities, including securities pledged, Fair Value	2,438		2,077
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	2		2
Fixed maturities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Fixed maturities, including securities pledged, Amortized Cost	49,903		50,021
Fixed maturities, Gross Unrealized Capital Gains	4,722		2,158
Fixed maturities, Gross Unrealized Capital Losses	201		1,084
Embedded Derivatives	29		26
Fixed maturities, including securities pledged, Fair Value	54,453		51,121
Total fixed maturities, less securities pledged, Amortized Cost	48,164		48,197
Total fixed maturities, less securities pledged, Gross Unrealized Capital Gains	4,503		2,051
Total fixed maturities, less securities pledged, Gross Unrealized Capital Losses	188		1,020
Total fixed maturities, less securities pledged, Fair Value	52,508		49,254
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	12		13
Impaired available-for-sale securities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Net unrealized gains on impaired available-for-sale securities	411	$ 300
Collateral Pledged
Available-for-sale Securities, Including Securities Pledged [Line Items]
Securities pledged	1,945		1,867
Collateral Pledged | Fixed maturities
Available-for-sale Securities, Including Securities Pledged [Line Items]
Embedded Derivatives	0		0
Securities pledged, Amortized Cost	1,739		1,824
Securities pledged, Gross Unrealized Capital Gains	219		107
Securities pledged, Gross Unrealized Capital Losses	13		64
Securities pledged	1,945		1,867
Accumulated Other Comprehensive Income (Loss), Other than Temporary Impairment, Not Credit Loss, Net of Tax, Debt Securities	$ 0		$ 0