Fair Value Measurements - Separate Account Assets (Details) - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014	Dec. 31, 2014
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		$ 520			$ 520			$ 530
Non-guaranteed separate accounts		7,388	[1]		7,388	[1]		7,798	[2]
Total separate account assets		7,908			7,908			8,328
Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Non-guaranteed separate accounts		3,700			3,700			3,800
Fair Value Inputs Level 1 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		226			226			242
Non-guaranteed separate accounts		1,409			1,409			1,609
Total separate account assets		1,635			1,635			1,851
Fair Value Inputs Level 2 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		294			294			288
Non-guaranteed separate accounts		4,762			4,762			5,031
Total separate account assets		5,056			5,056			5,319
Fair Value Inputs Level 3 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		0			0			0
Non-guaranteed separate accounts		1,217			1,217			1,158
Total separate account assets		1,217			1,217			1,158
Fair Value Inputs Level 3 [Member] | Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Non-guaranteed separate accounts		1,200			1,200			$ 1,100
Separate Account Assets [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		1,162		$ 1,074	1,158		$ 1,035
Policyholder gains (losses)	[3]	17		9	103		64
Purchases, issuances, settlements:
Purchases		40		24	137		148
Sales		0		0	0		(2)
Settlements		(15)		(29)	(191)		(173)
Total purchases, sales, settlements		25		(5)	(54)		(27)
Transfers into/(out of) Level 3:
Transfers into Level 3		16		1	17		14
Transfers out of Level 3		(3)		(5)	(7)		(12)
Total transfers into/(out of) Level 3		13		(4)	10		2
Ending Balance		1,217		1,074	1,217		1,074
Policyholder Gains Losses Attributable To Instruments Still Held		$ 17		$ 9	$ 103		$ 64

[1] As of September 30, 2015, non-guaranteed separate accounts included $3.7 billion in assets supporting the Company's pension plans, including $1.2 billion classified in Level 3.

[2] As of December 31, 2014, non-guaranteed separate accounts included $3.8 billion in assets supporting the Company's pension plans, including $1.1 billion classified in Level 3.

[3] Included in this amount are gains of $17 million and $103 million for the three months ended and nine months ended September 30, 2015 attributable to instruments still held at September 30, 2015 and gains of $9 million and $64 million for the three months ended and nine months ended September 30, 2014 attributable to instruments still held at September 30, 2014.