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Accounts Receivable, Net (Details) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2013
Dec. 31, 2012
Accounts, Notes, Loans and Financing Receivable [Line Items]    
Allowance for bill adjustments and uncollectible accounts $ 54 $ 48
Accounts receivable greater than 90 days old $ 50 $ 36