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Supplemental Cash Flow Information
 12 Months Ended
Dec. 31, 2017
Supplemental Cash Flow Information [Abstract]  
Supplemental Cash Flow Information
20. Supplemental Cash Flow Information
Year Ended December 31,
2017
2016
2015
(in millions)
Interest paid
$
165
 
$
162
 
$
182
 
Income tax payments
$
163
 
$
120
 
$
130
 
Income tax refunds
$
16
 
$
8
 
$
8