Fair Value Measurements - Changes in Level 3 Financial Assets (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Fixed Maturities And Equity Securities [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		$ 776	$ 726
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		0	0
Other		23	(25)
Total gains (losses) included in shareholders' net income		23	(25)
Gains (losses) included in other comprehensive income		(8)	0
Gains (losses) required to adjust future policy benefits for settlement annuities	[1]	0	11
Purchases, sales, and settlements:
Purchases		25	24
Sales		(47)	0
Settlements		(27)	(11)
Total purchases, sales, settlements		(49)	13
Transfers into/(out of) Level 3:
Transfers into Level 3		40	128
Transfers out of Level 3		(55)	(61)
Total transfers into/(out of) Level 3		(15)	67
Ending Balance		727	792
Total gains (losses) included in income attributable to instruments held at the reporting date		(6)	(25)
Derivative Financial Instruments, Assets [Member] | Guaranteed Minimum Income Benefit [Member]
Fair Value Assets Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance		799	907
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		(11)	61
Other		1	(1)
Total gains (losses) included in shareholders' net income		(10)	60
Gains (losses) included in other comprehensive income		0	0
Gains (losses) required to adjust future policy benefits for settlement annuities	[1]	0	0
Purchases, sales, and settlements:
Purchases		0	0
Sales		0	0
Settlements		(12)	(10)
Total purchases, sales, settlements		(12)	(10)
Transfers into/(out of) Level 3:
Transfers into Level 3		0	0
Transfers out of Level 3		0	0
Total transfers into/(out of) Level 3		0	0
Ending Balance		777	957
Total gains (losses) included in income attributable to instruments held at the reporting date		$ (10)	$ 60

[1] Amounts do not accrue to shareholders.