Fair Value Measurements - Changes in Level 3 Financial Liabilities (Details) - Derivative Financial Instruments, Liabilities [Member] - 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, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ (761)	$ (941)	$ (780)	$ (885)
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		(15)	(32)	(4)	(93)
Other		(3)	12	(7)	7
Total gains (losses) included in shareholders' net income		(18)	(20)	(11)	(86)
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		15	14	27	24
Total purchases, sales, and settlements		15	14	27	24
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		(764)	(947)	(764)	(947)
Total gains (losses) included in income attributable to instruments held at the reporting date		$ (18)	$ (20)	$ (11)	$ (86)

[1] Amounts do not accrue to shareholders.