Unaudited Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2012

Unaudited Quarterly Information [Abstract]

Quarterly financial data

Summarized quarterly financial data is as follows:

	Year Ended December 31, 2011
	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in millions)
Revenues	$	2,095	$	1,228	$	1,171	$	1,608
Operating income	260		114		111		177
Net income	133		47		43		93

	Year Ended December 31, 2012
	First Quarter		Second Quarter		Third Quarter			Fourth Quarter
	(in millions)
Revenues	$	1,550	$	846	$	954		$	1,551
Operating income (loss)	229		106		(152		)	211
Net income (loss)	118		42		(127		)	104