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		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance		$ (764)	$ (947)	$ (780)	$ (885)
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)		(40)	22	(44)	(71)
Other		6	(6)	(1)	1
Total gains (losses) included in shareholders' net income		(34)	16	(45)	(70)
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		18	23	45	47
Total purchases, sales, and settlements		18	23	45	47
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		(780)	(908)	(780)	(908)
Total gains (losses) included in income attributable to instruments held at the reporting date		$ (34)	$ 16	$ (45)	$ (70)

[1] Amounts do not accrue to shareholders.