Fair Value Measurements (Reconciliations For Change In Net Fair Value Of Derivative Assets And Liabilities Measured At Fair Value On A Recurring Basis Using Significant Unobservable Inputs (Level 3)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Fair Value Measurements [Abstract]
Balance at beginning of period	$ 3	$ (8)
Included in earnings	(162)	9
Settlements	(36)	2
Transfers into/out of Level 3
Balance at end of period	(195)	3
Change in gains (losses) included in earnings relating to derivatives still held as of December 31	$ (198)	$ 11