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Basis of Presentation and Summary of Significant Accounting Policies (Details 2) (USD $)
In Millions, unless otherwise specified
12 Months Ended
Dec. 31, 2014
segment
state
Dec. 31, 2013
Dec. 31, 2012
Schedule of Accounting Policies [Line Items]      
Number of states in which entity operates 14us-gaap_NumberOfStatesInWhichEntityOperates    
Revenue Recognition      
Term of indefeasible rights of use (in years) 20 years    
Advertising Costs      
Advertising expense $ 83us-gaap_AdvertisingExpense $ 88us-gaap_AdvertisingExpense $ 90us-gaap_AdvertisingExpense
Finite-Lived Intangible Assets, Net [Abstract]      
Number of reporting units (segment) 1us-gaap_NumberOfReportableSegments    
Number of Operating Segments 1us-gaap_NumberOfOperatingSegments    
Minimum      
Revenue Recognition      
Customer relationship period for revenue recognition (from eighteen months to over ten years) 18 months    
Accounts Receivable, Net [Abstract]      
Period accounts receivable are past due 30 days    
Maximum      
Revenue Recognition      
Customer relationship period for revenue recognition (from eighteen months to over ten years) 10 years    
Customer relationships      
Finite-Lived Intangible Assets, Net [Abstract]      
Finite-Lived Intangible Asset, Useful Life 10 years    
Capitalized software | Maximum      
Finite-Lived Intangible Assets, Net [Abstract]      
Finite-Lived Intangible Asset, Useful Life 7 years