Fair Value Measurements - Changes in Level 3 Financial Liabilities (Details) - Derivative Financial Instruments, Liabilities [Member] - Guaranteed Minimum Income Benefit [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning balance	$ (780)	$ (885)
Gains (losses) included in shareholders' net income:
GMIB fair value gain/(loss)	(31)	47
Other	(5)	(3)
Total gains (losses) included in shareholders' net income	(36)	44
Gains (losses) included in other comprehensive income	0	0
Gains (losses) required to adjust future policy benefits for settlement annuities	0	0
Purchases, sales, settlements:
Purchases	0	0
Sales	0	0
Settlements	54	61
Total purchases, sales, and settlements	54	61
Transfers into/(out of) Level 3:
Transfers into Level 3	0	0
Transfers out of Level 3	0	0
Transfers into/(out of) Level 3	0	0
Ending balance	(762)	(780)
Total gains (losses) included in income attributable to instruments held at the reporting date	$ (36)	$ 44