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
	Mar. 31, 2016	Mar. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	$ (21)	$ (21)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	7	35
Total gain (loss) on derivatives	(14)	14
Basis Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	(3)	(8)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	4	(6)
Sold Call Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	(50)	8
Purchased Put Options [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	15
Fixed Price Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	20	(18)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	4	42
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative Instrument, Gain (Loss) on Derivatives, Unsettled	(3)	(3)
Derivative Instrument, Gain (Loss) on Derivatives, Settled	$ (1)	$ (1)