Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016		Dec. 31, 2015
Financial assets at fair value:
Fixed maturities	$ 20,961		$ 19,455
Equity securities	583		190
Short-term investments	691		381
Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	20,961	[1]	19,455	[2]
Equity securities	583		190
Subtotal	21,544		19,645
Short-term investments	691		381
Total financial assets at fair value, excluding separate accounts	23,044		20,949
Financial liabilities at fair value:
Total financial liabilities at fair value	785		885
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	524		483
Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	10		16
Financial liabilities at fair value:
Derivative liabilities	5
Guaranteed Minimum Income Benefit [Member]
Financial assets at fair value:
Derivative assets	799		907
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	799		907
Financial liabilities at fair value:
Derivative liabilities	780		885
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	877		779
State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,435		1,641
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,113		2,014
Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	16,050		14,448
Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	486		573
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	374	[1]	251	[2]
Equity securities	396		32
Subtotal	770		283
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	770		283
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		0
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		0
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	374		251
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 and 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	19,885	[1]	18,547	[2]
Equity securities	113		89
Subtotal	19,998		18,636
Short-term investments	691		381
Total financial assets at fair value, excluding separate accounts	20,699		19,033
Financial liabilities at fair value:
Total financial liabilities at fair value	5		0
Fair Value Inputs Level 2 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	10		16
Financial liabilities at fair value:
Derivative liabilities	5
Fair Value Inputs Level 2 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0		0
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	503		528
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,435		1,641
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,066		2,010
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	15,552		14,122
Fair Value Inputs Level 2 [Member] | Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	329		246
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	702	[1]	657	[2]
Equity securities	74		69
Subtotal	776		726
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	1,575		1,633
Financial liabilities at fair value:
Total financial liabilities at fair value	780		885
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	14		30
Fair Value Inputs Level 3 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	0		0
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	799		907
Financial liabilities at fair value:
Derivative liabilities	780		885
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	47		4
Fair Value Inputs Level 3 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	498		326
Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	$ 157		$ 327

[1] Fixed maturities included $524 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $14 million of appreciation for securities classified in Level 3. See Note 11A for additional information.

[2] Fixed maturities included $483 million of net 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 11A for additional information.