Fair Value Measurements - Changes in Level 3 Financial Assets (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fixed Maturities And Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 743	$ 666	$ 726	$ 857
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		0	0	0	0
Other		0	1	(16)	29
Total gains (losses) included in shareholders' net income		0	1	(16)	29
Gains (losses) included in other comprehensive income		12	(1)	11	(18)
Gains (losses) required to adjust future policy benefits for settlement annuities	[1]	0	4	35	6
Purchases, sales, and settlements:
Purchases		20	25	67	136
Sales		(1)	(1)	(126)	(229)
Settlements		(55)	(13)	(71)	(20)
Total purchases, sales, settlements		(36)	11	(130)	(113)
Transfers into/(out of) Level 3:
Transfers into Level 3		44	48	235	49
Transfers out of Level 3		(30)	(8)	(128)	(89)
Total transfers into/(out of) Level 3		14	40	107	(40)
Ending Balance		733	721	733	721
Total gains (losses) included in income attributable to instruments held at the reporting date		0	(1)	(11)	(1)
Derivative Financial Instruments, Assets [Member] | Guaranteed Minimum Income Benefit [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		975	867	907	953
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		(22)	104	71	37
Other		1	0	0	0
Total gains (losses) included in shareholders' net income		(21)	104	71	37
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		(23)	(10)	(47)	(29)
Total purchases, sales, settlements		(23)	(10)	(47)	(29)
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		931	961	931	961
Total gains (losses) included in income attributable to instruments held at the reporting date		$ (21)	$ 104	$ 71	$ 37

[1] Amounts do not accrue to shareholders.