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Unaudited Quarterly Information
12 Months Ended
Dec. 31, 2017
Unaudited Quarterly Information [Abstract]  
Unaudited Quarterly Information [Text Block]
Unaudited Quarterly Information

Summarized quarterly financial data is as follows:
 
Year Ended December 31, 2017
 
First
Quarter
 
Second
Quarter
 
Third
Quarter
 
Fourth
Quarter
 
(in millions)
Revenues
$
2,093

 
$
1,387

 
$
1,251

 
$
1,872

Operating income
194

 
53

 
26

 
171

Net income (1)
147

 
54

 
38

 
506

 
Year Ended December 31, 2016
 
First
Quarter
 
Second
Quarter
 
Third
Quarter
 
Fourth
Quarter
 
(in millions)
Revenues
$
1,320

 
$
807

 
$
978

 
$
1,349

Operating income
166

 
18

 
26

 
108

Net income
120

 
6

 
43

 
76


(1)
Net income for the fourth quarter 2017 includes a reduction in income taxes of $396 million due to tax reform. See Note 13 for further discussion of the impacts of tax reform implementation.