Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) $ in Millions	9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($)		Dec. 31, 2014 USD ($)
Financial assets at fair value:
Fixed maturities	$ 18,747		$ 18,983
Equity securities	184		189
Short-term investments	94		163
Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	18,747	[1]	18,983	[2]
Equity securities	184		189
Subtotal	18,931		19,172
Short-term investments	94		163
Total financial assets at fair value, excluding separate accounts	20,002		20,294
Financial liabilities at fair value:
Total financial liabilities at fair value	936		930
Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]
Financial liabilities at fair value:
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities	592		756
Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	16	[3]	6	[4]
Financial liabilities at fair value:
Derivative liabilities	1		1
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	$ 16		5
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Fair Value Hedging [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets			$ 1
Guaranteed Minimum Income Benefit [Member]
Financial liabilities at fair value:
Number of external reinsurers	3		3
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	$ 961	[5]	$ 953	[6]
Financial liabilities at fair value:
Derivative liabilities	935		929
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	861		954
State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,717		1,856
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,950		1,940
Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	13,624		13,498
Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	55		85
Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	540		650
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	258	[1]	290	[2]
Equity securities	33		61
Subtotal	291		351
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	291		351
Financial liabilities at fair value:
Total financial liabilities at fair value	0		0
Fair Value Inputs Level 1 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0	[3]	0	[4]
Financial liabilities at fair value:
Derivative liabilities	0		0
Fair Value Inputs Level 1 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0	[5]	0	[6]
Financial liabilities at fair value:
Derivative liabilities	0		0
Fair Value Inputs Level 1 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	258		290
Fair Value Inputs Level 1 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 1 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 1 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 1 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 1 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 2 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	17,820	[1]	17,879	[2]
Equity securities	99		85
Subtotal	17,919		17,964
Short-term investments	94		163
Total financial assets at fair value, excluding separate accounts	18,029		18,133
Financial liabilities at fair value:
Total financial liabilities at fair value	1		1
Fair Value Inputs Level 2 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	16	[3]	6	[4]
Financial liabilities at fair value:
Derivative liabilities	1		1
Fair Value Inputs Level 2 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0	[5]	0	[6]
Financial liabilities at fair value:
Derivative liabilities	0		0
Fair Value Inputs Level 2 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	603		664
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,717		1,856
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,946		1,936
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	13,299		13,105
Fair Value Inputs Level 2 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	54		84
Fair Value Inputs Level 2 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	201		234
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	669	[1]	814	[2]
Equity securities	52		43
Subtotal	721		857
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	1,682		1,810
Financial liabilities at fair value:
Total financial liabilities at fair value	935		929
Fair Value Inputs Level 3 [Member] | Run-off Settlement Annuity Business [Member] | Fair Value, Measurements, Recurring [Member]
Financial liabilities at fair value:
Net appreciation required to adjust future policy benefits for run-off settlement annuity business included in fixed maturities	37		65
Fair Value Inputs Level 3 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0	[3]	0	[4]
Financial liabilities at fair value:
Derivative liabilities	0		0
Fair Value Inputs Level 3 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	961	[5]	953	[6]
Financial liabilities at fair value:
Derivative liabilities	935		929
Fair Value Inputs Level 3 [Member] | Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 3 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	0		0
Fair Value Inputs Level 3 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	4		4
Fair Value Inputs Level 3 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	325		393
Fair Value Inputs Level 3 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1		1
Fair Value Inputs Level 3 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	$ 339		$ 416

[1] Fixed maturities included $592 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $37 million of appreciation for securities classified in Level 3. See Note 9 for additional information.

[2] Fixed maturities included $756 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $65 million of appreciation for securities classified in Level 3. See Note 9 for additional information.

[3] Other derivative assets reflected interest rate and foreign currency swaps qualifying as cash flow hedges. See Note 10 for additional information.

[4] Other derivative assets included $5 million of interest rate and foreign currency swaps qualifying as cash flow hedges and $1 million of interest rate swaps qualifying as fair value hedges. See Note 10 for additional information.

[5] The GMIB assets represent retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.

[6] The GMIB assets represented retrocessional contracts in place from three external reinsurers that cover the exposures on these contracts.