Fair Value Measurements - Changes in Level 3 Net Derivative Assets (Liabilities) (Details) - Guaranteed Minimum Income Benefit [Member] - USD ($) $ in Millions		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Fair Value, Net Derivative Asset (Liability), Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ 16	$ 16	$ 19	$ 22
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		0	0	0	0
Other		(3)	12	(6)	6
Total gains (losses) included in shareholders' net income		(3)	12	(6)	6
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, settlements:
Purchases		0	0	0	0
Sales		0	0	0	0
Settlements		0	0	0	0
Total purchases, sales, settlements		0	0	0	0
Transfers into/(out of) Level 3:
Transfers into Level 3		0	0	0	0
Transfers out of Level 3		0	0	0	0
Transfers into/out of Level 3		0	0	0	0
Ending balance		13	28	13	28
Total gains (losses) included in income attributable to instruments held at the reporting date		$ (3)	$ 12	$ (6)	$ 6

[1] Amounts do not accrue to shareholders.