Derivatives And Risk Management (Summary Of Before Tax Effect Of Fair Value Hedges Not Designated For Hedge Accounting) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Basis Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Net of Settlement	$ (2)	$ (7)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	(2)	12
Fixed Price Call Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Net of Settlement	13	18
Fixed Price Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Net of Settlement	(164)	126
Derivative Instrument, Gain (Loss) on Derivatives, Settled	208	(2)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Net of Settlement	(2)	(7)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	$ (4)	$ (1)