Fair Value Measurements - Separate Account Assets (Details) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2015		Jun. 30, 2014	Jun. 30, 2015		Jun. 30, 2014	Dec. 31, 2014
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		$ 552			$ 552			$ 530
Non-guaranteed separate accounts		7,759	[1]		7,759	[1]		7,798	[2]
Total separate account assets		8,311			8,311			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		239			239			242
Non-guaranteed separate accounts		1,656			1,656			1,609
Total separate account assets		1,895			1,895			1,851
Fair Value Inputs Level 2 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		313			313			288
Non-guaranteed separate accounts		4,941			4,941			5,031
Total separate account assets		5,254			5,254			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		1,162			1,162			1,158
Total separate account assets		1,162			1,162			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		1,100			1,100			$ 1,100
Separate Account Assets [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		1,095		$ 1,069	1,158		$ 1,035
Policyholder gains (losses)	[3]	53		23	86		55
Purchases, issuances, settlements:
Purchases		60		80	97		124
Sales		0		(2)	0		(2)
Settlements		(47)		(97)	(176)		(144)
Total purchases, sales, settlements		13		(19)	(79)		(22)
Transfers into/(out of) Level 3:
Transfers into Level 3		1		6	1		13
Transfers out of Level 3		0		(5)	(4)		(7)
Total transfers into/(out of) Level 3		1		1	(3)		6
Ending Balance		1,162		1,074	1,162		1,074
Policyholder Gains Losses Attributable To Instruments Still Held		$ 52		$ 23	$ 84		$ 55

[1] As of June 30, 2015, non-guaranteed separate accounts included $3.7 billion in assets supporting the Company's pension plans, including $1.1 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 $52 million and $84 million for the three months ended and six months ended June 30, 2015 attributable to instruments still held at June 30, 2015 and gains of $23 million and $55 million for the three months ended and six months ended June 30, 2014 attributable to instruments still held at June 30, 2014.