Derivative Financial Instruments (Hedges) (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended	12 Months Ended		6 Months Ended
	Jun. 30, 2013 Cash Flow Hedges [Member]	Dec. 31, 2012 Cash Flow Hedges [Member]	Jun. 30, 2012 Cash Flow Hedges [Member]	Jun. 30, 2013 Fair Value Hedges [Member]	Jun. 30, 2012 Fair Value Hedges [Member]
Unrealized net gains (losses) on cash flow hedges, after tax	$ 11	$ 173
Estimated amount in accumulated other comprehensive income expected to be reclassified within twelve months, after tax	(46)	(37)
Pre-tax deferred gain from terminated fair value hedges				0	90
Pre-tax benefits from reductions of interest expense from previous hedge unwinds				44	164
Pre-tax Deferred Gain From Terminated Cash Flow Hedges Recorded In OCI	$ 198		$ 0