Derivatives And Risk Management (Summary Of Before Tax Effect Of Fair Value Hedges Not Designated For Hedge Accounting) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Basis Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	$ 3	$ (3)	$ (5)	$ (13)
Derivative Instruments, Gain (Loss) on Derivatives, Settled		5	(6)	(10)
Fixed Price Call Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled		4	8	(23)
Fixed Price Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	(55)	2	(73)	(21)
Derivative Instruments, Gain (Loss) on Derivatives, Settled	52	(13)	94	(36)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	2	$ (3)	(1)	$ (5)
Derivative Instruments, Gain (Loss) on Derivatives, Settled	$ (1)		$ (2)