Financial Instruments (Effect of Cash Flows Hedges on Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Derivative [Line Items]
Additions and revaluations of derivatives designated as cash flow hedges	$ (9)	$ (2)
Portion of ending balance expected to be reclassified into earnings over the next twelve months, after-tax	14
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning balance	3	41
Additions and revaluations of derivatives designated as cash flow hedges	(9)	(4)
Ending balance	(12)	18
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Portion Attributable to Parent	$ (6)	$ (19)