Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)		Dec. 31, 2014 USD ($)
Financial assets at fair value:
Fixed maturities	$ 19,455		$ 18,983
Equity securities	190		189
Short-term investments	381		163
Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	19,455	[1]	18,983	[2]
Equity securities	190		189
Subtotal	19,645		19,172
Short-term investments	381		163
Total financial assets at fair value, excluding separate accounts	20,949		20,294
Financial liabilities at fair value:
Total financial liabilities at fair value	885		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	483		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
Other derivatives [Member] | Designated as Hedging Instrument [Member] | Cash Flow Hedging [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	15		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		$ 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	$ 907	[5]	$ 953	[6]
Financial liabilities at fair value:
Derivative liabilities	885		929
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	779		954
State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,641		1,856
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,014		1,940
Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	14,448		13,498
Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	49		85
Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	524		650
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	251	[1]	290	[2]
Equity securities	32		61
Subtotal	283		351
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	283		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
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	251		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	18,547	[1]	17,879	[2]
Equity securities	89		85
Subtotal	18,636		17,964
Short-term investments	381		163
Total financial assets at fair value, excluding separate accounts	19,033		18,133
Financial liabilities at fair value:
Total financial liabilities at fair value	0		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
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	528		664
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,641		1,856
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,010		1,936
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	14,122		13,105
Fair Value Inputs Level 2 [Member] | Mortgage-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	48		84
Fair Value Inputs Level 2 [Member] | Other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	198		234
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	657	[1]	814	[2]
Equity securities	69		43
Subtotal	726		857
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	1,633		1,810
Financial liabilities at fair value:
Total financial liabilities at fair value	885		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	30		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
Fair Value Inputs Level 3 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	907	[5]	953	[6]
Financial liabilities at fair value:
Derivative liabilities	885		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	326		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	$ 326		$ 416

[1] Fixed maturities included $483 million of net cumulative appreciation required to adjust future policy benefits for the run-off settlement annuity business including $30 million of appreciation for securities classified in Level 3. See Note 11 for additional information.

[2] Fixed maturities included $756 million of net cumulative 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 11 for additional information.

[3] Other derivative assets included $15 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 12 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 12 for additional information.

[5] The GMIB assets represented 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.