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Depreciation and Amortization Expense (Details) (USD $)
In Millions, unless otherwise specified
3 Months Ended
Mar. 31, 2012
Mar. 31, 2011
Depreciation And Amortization Expense (Textual) [Abstract]    
Depreciation and amortization expense $ 55 $ 75
Accelerated depreciation $ 7 $ 19