Derivatives (Net Derivative Gains Losses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Components of Net Derivatives Gains (Losses)
Derivatives and hedging gains (losses)	$ (1,389)	$ (509)	$ 429
Embedded derivatives gains (losses)	799	(181)	200
Total net derivative gains (losses)	$ (590)	$ (690)	$ 629