Fair Value Measurements - Separate Account Assets (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		$ 509		$ 530
Non-guaranteed separate accounts		7,324	[1]	7,798	[2]
Total separate account assets		7,833		8,328
Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Non-guaranteed separate accounts		3,600		3,800
Fair Value Inputs Level 1 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		235		242
Non-guaranteed separate accounts		1,401		1,609
Total separate account assets		1,636		1,851
Fair Value Inputs Level 2 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		274		288
Non-guaranteed separate accounts		4,698		5,031
Total separate account assets		4,972		5,319
Fair Value Inputs Level 3 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		0		0
Non-guaranteed separate accounts		1,225		1,158
Total separate account assets		1,225		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		1,100
Separate Account Assets [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		1,158		1,035
Policyholder gains (losses)	[3]	95		85
Purchases, issuances, settlements:
Purchases		198		266
Sales		0		(2)
Settlements		(230)		(226)
Total purchases, sales, settlements		(32)		38
Transfers into/(out of) Level 3:
Transfers into Level 3		16		20
Transfers out of Level 3		(12)		(20)
Total transfers into/(out of) Level 3		4		0
Ending Balance		1,225		1,158
Policyholder Gains Losses Attributable To Instruments Still Held		$ 95		$ 85

[1] As of December 31, 2015, non-guaranteed separate accounts included $3.6 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 were gains of $95 million attributable to instruments still held at December 31, 2015 and gains of $85 million attributable to instruments still held at December 31, 2014.