Derivatives And Risk Management (Summary Of Before Tax Effect Of Fair Value Hedges Not Designated For Hedge Accounting) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Basis Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	$ (8)	$ (10)
Derivative Instruments, Gain (Loss) on Derivatives, Settled	(6)	(14)
Fixed Price Call Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	8	(27)
Fixed Price Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	(18)	(23)
Derivative Instruments, Gain (Loss) on Derivatives, Settled	42	(24)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	(3)	(2)
Derivative Instruments, Gain (Loss) on Derivatives, Settled	$ (1)