Derivatives and Other Hedging Instruments (Effect of Cash Flow Hedges on Accumulated Other Comprehensive Income (Loss)) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Derivative [Line Items]
Portion of ending balance of gain (loss) expected to be reclassified into earnings over the next twelve months, after-tax	$ (6)
Cash Flow Hedging [Member]
Derivative [Line Items]
Beginning balance, after-tax		(48)	3
Additions and revaluations of derivatives designated as cash flow hedges, after-tax		33	(36)
Clearance of hedge results to earnings, after-tax		9	(15)
Ending balance, after-tax		$ (6)	$ (48)