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Summary of Significant Accounting Policies Summary of Significant Accounting Policies (Tables)
 12 Months Ended
Dec. 31, 2014
Accounting Policies [Abstract]  
Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]
The change in the balance of the allowance for doubtful accounts, which is included in accounts receivable, net on the Consolidated Balance Sheets, is summarized as follows for the years ended December 31 (in millions):

 
2014
 
2013
 
2012
 
 
 
 
 
 
Beginning balance
$
8

 
$
9

 
$
9

Charged to operating costs and expenses, net
11

 
13

 
14

Write-offs, net
(12
)
 
(14
)
 
(14
)
Ending balance
$
7

 
$
8

 
$
9