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		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Basis Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	$ 1	$ (3)	$ (4)	$ (16)
Derivative Instruments, Gain (Loss) on Derivatives, Settled		9	(6)
Fixed Price Call Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	3	11	11	(11)
Fixed Price Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	(37)	45	(110)	24
Derivative Instruments, Gain (Loss) on Derivatives, Settled	49	15	143	(21)
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instruments, Gain (Loss) on Derivatives, Excluding Derivatives, Settled	$ (1)	$ 1	(2)	(4)
Derivative Instruments, Gain (Loss) on Derivatives, Settled			$ (2)	$ (1)