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		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value Measurements [Abstract]
Balance at beginning of period	$ (83)	$ (5)	$ 3	$ (8)
Included in earnings	58	4	(13)	1
Purchases, issuances, and settlements:
Settlements			(15)	6
Transfers into/out of Level 3
Balance at end of period	(25)	(1)	(25)	(1)
Change in gains (losses) included in earnings relating to derivatives still held as of September 30	$ 58	$ 4	$ (28)	$ 7