Unaudited Quarterly Information Unaudited Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2015

Unaudited Quarterly Information [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

Summarized quarterly financial data is as follows:

	Year Ended December 31, 2015
	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in millions)
Revenues	$	617	$	705	$	827	$	697
Operating income	101		158		244		105
Net income	31		69		124		37

	Year Ended December 31, 2014
	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in millions)
Revenues	$	630	$	698	$	839	$	679
Operating income	106		145		232		113
Net income	35		57		119		41