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	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Fair Value Measurements [Abstract]
Balance at beginning of period	$ (35)	$ (8)	$ 3	$ (8)
Included in earnings	(37)	3	(71)	(3)
Purchases, issuances, and settlements:
Settlements	(11)		(15)	6
Transfers into/out of Level 3
Balance at end of period	(83)	(5)	(83)	(5)
Change in gains (losses) included in earnings relating to derivatives still held as of June 30	$ (48)	$ 3	$ (86)	$ 3