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Stock-Based Compensation (Tables)
3 Months Ended
Mar. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-Based Compensation
Stock-based compensation for the three months ended March 31 is as follows:
(in millions)
2015
 
2014
Stock option expense
$
6

 
$
3

Restricted stock and unit awards expense
12

 
14

Total stock-based compensation expense 
$
18

 
$
17