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Stock-Based Compensation Stock-Based Compensation Expense (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2014
Jun. 30, 2013
Jun. 30, 2014
Jun. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]        
Stock-based compensation expense $ 1 $ 2 $ 2 $ 3