Fair Value Measurements - Financial Assets and Financial Liabilities Carried at Fair Value (Details) - USD ($) $ in Millions	6 Months Ended		12 Months Ended
	Jun. 30, 2017		Dec. 31, 2016
Financial assets at fair value:
Fixed maturities	$ 22,513		$ 20,961
Equity securities	635		583
Short-term investments	138		691
Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	22,513	[1]	20,961	[2]
Equity securities	635		583
Subtotal	23,148		21,544
Short-term investments	138		691
Total financial assets at fair value, excluding separate accounts	24,066		23,044
Financial liabilities at fair value:
Total financial liabilities at fair value	771		785
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	627		524
Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	3		10
Financial liabilities at fair value:
Derivative liabilities	7		5
Guaranteed Minimum Income Benefit [Member]
Financial assets at fair value:
Derivative assets	777		799
Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	777		799
Financial liabilities at fair value:
Derivative liabilities	764		780
Federal government and agency [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	900		877
State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,381		1,435
Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,313		2,113
Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	17,436		16,050
Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	483		486
Fair Value Inputs Level 1 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	379	[1]	374	[2]
Equity securities	410		396
Subtotal	789		770
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	789		770
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		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	379		374
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	21,492	[1]	19,885	[2]
Equity securities	116		113
Subtotal	21,608		19,998
Short-term investments	138		691
Total financial assets at fair value, excluding separate accounts	21,749		20,699
Financial liabilities at fair value:
Total financial liabilities at fair value	7		5
Fair Value Inputs Level 2 [Member] | Other derivatives [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	3		10
Financial liabilities at fair value:
Derivative liabilities	7		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	521		503
Fair Value Inputs Level 2 [Member] | State and local government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	1,381		1,435
Fair Value Inputs Level 2 [Member] | Foreign government [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	2,274		2,066
Fair Value Inputs Level 2 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	16,982		15,552
Fair Value Inputs Level 2 [Member] | Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	334		329
Fair Value Inputs Level 3 [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	642	[1]	702	[2]
Equity securities	109		74
Subtotal	751		776
Short-term investments	0		0
Total financial assets at fair value, excluding separate accounts	1,528		1,575
Financial liabilities at fair value:
Total financial liabilities at fair value	764		780
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	18		14
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		0
Fair Value Inputs Level 3 [Member] | Guaranteed Minimum Income Benefit [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Derivative assets	777		799
Financial liabilities at fair value:
Derivative liabilities	764		780
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	39		47
Fair Value Inputs Level 3 [Member] | Corporate [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	454		498
Fair Value Inputs Level 3 [Member] | Mortgage and other asset-backed [Member] | Fair Value, Measurements, Recurring [Member]
Financial assets at fair value:
Fixed maturities	$ 149		$ 157

[1] Fixed maturities includes $627 million of net appreciation required to adjust future policy benefits for the run-off settlement annuity business including $18 million of appreciation for securities classified in Level 3. See Note 10 for additional information.

[2] Fixed maturities includes $524 million of net appreciation required to adjust future policy benefits for run-off settlement annuity business including $14 million of appreciation for securities classified in Level 3. See Note 10 for additional information.