Fair Value Measurements - Separate Account Assets (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		$ 504		$ 509
Non-guaranteed separate accounts	[1]	6,551		6,396
Subtotal		7,055		6,905
Non-guaranteed separate accounts priced at NAV as a practical expedient	[1]	930		928
Total separate account assets		7,985		7,833
Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Non-guaranteed separate accounts priced at NAV as a practical expedient		900		900
Non-guaranteed separate accounts		3,600		3,600
Fair Value Inputs Level 1 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		231		235
Non-guaranteed separate accounts		1,372		1,401
Subtotal		1,603		1,636
Fair Value Inputs Level 2 [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Guaranteed separate accounts		273		274
Non-guaranteed separate accounts		4,862		4,698
Subtotal		5,135		4,972
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]	317		297
Subtotal		317		297
Fair Value Inputs Level 3 [Member] | Pension Benefits [Member]
Financial assets and financial liabilities carried at fair value [Line Items]
Non-guaranteed separate accounts		300		$ 300
Separate Account Assets [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		297	$ 255
Policyholder gains (losses)		(1)	1
Purchases, sales, and settlements:
Purchases		4	10
Sales		(1)	0
Settlements		(2)	(3)
Total purchases, sales, and settlements		1	7
Transfers into/(out of) Level 3:
Transfers into Level 3		23	0
Transfers out of Level 3		(3)	(4)
Total transfers into/(out of) Level 3		20	(4)
Ending Balance		$ 317	$ 259

[1] Non-guaranteed separate accounts as of March 31, 2016 and December 31, 2015 included $3.6 billion in assets supporting the Company's pension plans, with $0.3 billion classified in Level 3 and $0.9 billion priced at NAV as a practical expedient.