Derivatives (Changes in Estimated Fair Value Related to Embedded Derivatives) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Net derivative gains (losses)
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gains (losses)	$ 1,237	$ (1,741)	$ (344)
Policyholder Benefits And Claims Incurred Net [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Net derivatives gains (losses)	$ (16)	$ (4)	$ 21