Unaudited Quarterly Information Unaudited Quarterly Information (Tables)

12 Months Ended

Dec. 31, 2012

Unaudited Quarterly Information [Abstract]

Schedule of Quarterly Financial Information [Table Text Block]

Summarized quarterly financial data is as follows:

	Year Ended December 31, 2011
	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in millions)
Revenues	$	489	$	606	$	707	$	535
Operating income	101		185		244		93
Income before extraordinary item (1)	24		79		367		18
Extraordinary item, net of tax (1)	—		—		598		—
Net income	24		79		965		18

(1) During the third quarter of 2011, CenterPoint Energy recorded an extraordinary gain of $598 million, after-tax, related to the Final Order and a $229 million, after-tax, return on true-up balance included in Income before extraordinary item related to a portion of interest on the appealed amount as discussed in Note 4(b).

	December 31, 2012
	First Quarter		Second Quarter		Third Quarter		Fourth Quarter
	(in millions, except per share amounts)
Revenues	$	531	$	676	$	748	$	585
Operating income	107		191		242		99
Net income	36		78		138		27