Fair Value Measurements - Changes in Level 3 Net Derivative Assets (Liabilities) (Details) - Guaranteed Minimum Income Benefit [Member] - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Net Derivative Asset (Liability), Measured On Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance		$ 13	$ 28	$ 19	$ 22
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		0	0	0	0
Other		5	(5)	(1)	1
Total gains (losses) included in shareholders' net income		5	(5)	(1)	1
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		18	23	18	23
Total gains (losses) included in income attributable to instruments held at the reporting date		$ 5	$ (5)	$ (1)	$ 1

[1] Amounts do not accrue to shareholders.