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Stock-Based Compensation (Tables)
 6 Months Ended
Jun. 30, 2013
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Stock-Based Compensation
Stock-based compensation for the periods ended June 30 is as follows:
(in millions)
Three Months
 
Six Months
 
2013
 
2012
 
2013
 
2012
Stock option expense
$
4

 
$
2

 
$
6

 
$
7

Restricted stock and unit awards expense
22

 
21

 
41

 
33

Total stock-based compensation expense
$
26

 
$
23

 
$
47

 
$
40