Fair Value Measurements - Changes in Level 3 Financial Assets (Details) - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fixed Maturities And Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 792	$ 818	$ 726	$ 857
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		0	0	0	0
Other		9	15	(16)	28
Total gains (losses) included in shareholders' net income		9	15	(16)	28
Gains (losses) included in other comprehensive income		(1)	(19)	(1)	(17)
Gains (losses) required to adjust future policy benefits for settlement annuities	[1]	24	(4)	35	2
Purchases, sales, and settlements:
Purchases		23	100	47	111
Sales		(125)	(210)	(125)	(228)
Settlements		(5)	(4)	(16)	(7)
Total purchases, sales, settlements		(107)	(114)	(94)	(124)
Transfers into/(out of) Level 3:
Transfers into Level 3		63	0	191	1
Transfers out of Level 3		(37)	(30)	(98)	(81)
Total transfers into/(out of) Level 3		26	(30)	93	(80)
Ending Balance		743	666	743	666
Total gains (losses) included in income attributable to instruments held at the reporting date		(1)	0	(23)	0
Derivative Financial Instruments, Assets [Member] | Guaranteed Minimum Income Benefit [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		957	970	907	953
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		32	(94)	93	(67)
Other		0	1	(1)	0
Total gains (losses) included in shareholders' net income		32	(93)	92	(67)
Gains (losses) included in other comprehensive income		0	0	0	0
Gains (losses) required to adjust future policy benefits for settlement annuities	[1]	0	0	0	0
Purchases, sales, and settlements:
Purchases		0	0	0	0
Sales		0	0	0	0
Settlements		(14)	(10)	(24)	(19)
Total purchases, sales, settlements		(14)	(10)	(24)	(19)
Transfers into/(out of) Level 3:
Transfers into Level 3		0	0	0	0
Transfers out of Level 3		0	0	0	0
Total transfers into/(out of) Level 3		0	0	0	0
Ending Balance		975	867	975	867
Total gains (losses) included in income attributable to instruments held at the reporting date		$ 32	$ (93)	$ 92	$ (67)

[1] Amounts do not accrue to shareholders.