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
	Mar. 31, 2016	Mar. 31, 2015
Fair Value Measurements [Abstract]
Balance at beginning of period	$ 3	$ (8)
Included in earnings	(34)	(6)
Purchases, issuances, and settlements:
Settlements	$ (4)	$ 6
Transfers into/out of Level 3
Balance at end of period	$ (35)	$ (8)
Change in losses included in earnings relating to derivatives still held as of March 31	$ (38)