Derivatives (Fair Value Hedges) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	$ (14)	$ (56)	$ (300)
Net Derivative Gains (Losses) Recognized for Hedged Items	104	42	286
Ineffectiveness Recognized in Net Derivative Gains (Losses)	90	(14)	(14)
Interest rate swaps | Fixed Maturity Securities
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	4	7	4
Net Derivative Gains (Losses) Recognized for Hedged Items	(4)	(9)	(1)
Ineffectiveness Recognized in Net Derivative Gains (Losses)	0	(2)	3
Interest rate swaps | Policyholder account balances [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	(69)	(108)	(4)
Net Derivative Gains (Losses) Recognized for Hedged Items	134	90	(6)
Ineffectiveness Recognized in Net Derivative Gains (Losses)	65	(18)	(10)
Foreign currency swaps | Foreign-denominated fixed maturity securities
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	(27)	13	15
Net Derivative Gains (Losses) Recognized for Hedged Items	29	(12)	(7)
Ineffectiveness Recognized in Net Derivative Gains (Losses)	2	1	8
Foreign currency swaps | Foreign-denominated policyholder account balances [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	65	(95)	(240)
Net Derivative Gains (Losses) Recognized for Hedged Items	(44)	92	232
Ineffectiveness Recognized in Net Derivative Gains (Losses)	21	(3)	(8)
Foreign currency forwards | Foreign-denominated fixed maturity securities
Derivative Instruments, Gain (Loss) [Line Items]
Net Derivative Gains (Losses) Recognized for Derivatives	13	127	(75)
Net Derivative Gains (Losses) Recognized for Hedged Items	(11)	(119)	68
Ineffectiveness Recognized in Net Derivative Gains (Losses)	$ 2	$ 8	$ (7)