Reportable Business Segments (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended			3 Months Ended			6 Months Ended				3 Months Ended			6 Months Ended				3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended						2 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012	Dec. 31, 2012	Jun. 30, 2013 Natural Gas Distribution [Member]	Jun. 30, 2012 Natural Gas Distribution [Member]	Jun. 30, 2013 Natural Gas Distribution [Member]	Jun. 30, 2012 Natural Gas Distribution [Member]	Dec. 31, 2012 Natural Gas Distribution [Member]	Jun. 30, 2013 Competitive Natural Gas Sales and Services [Member]	Jun. 30, 2012 Competitive Natural Gas Sales and Services [Member]	Jun. 30, 2013 Competitive Natural Gas Sales and Services [Member]	Jun. 30, 2012 Competitive Natural Gas Sales and Services [Member]	Dec. 31, 2012 Competitive Natural Gas Sales and Services [Member]	Jun. 30, 2013 Interstate Pipelines [Member]		Jun. 30, 2012 Interstate Pipelines [Member]	Jun. 30, 2013 Interstate Pipelines [Member]		Jun. 30, 2012 Interstate Pipelines [Member]	Dec. 31, 2012 Interstate Pipelines [Member]	Jun. 30, 2013 Field Services [Member]		Jun. 30, 2012 Field Services [Member]	Jun. 30, 2013 Field Services [Member]		Jun. 30, 2012 Field Services [Member]	Dec. 31, 2012 Field Services [Member]	Jun. 30, 2013 Midstream Investments [Member]		Jun. 30, 2013 Midstream Investments [Member]		Jun. 30, 2013 Other Operations [Member]	Jun. 30, 2012 Other Operations [Member]	Jun. 30, 2013 Other Operations [Member]	Jun. 30, 2012 Other Operations [Member]	Dec. 31, 2012 Other Operations [Member]	Jun. 30, 2013 Reconciling Eliminations [Member]	Jun. 30, 2012 Reconciling Eliminations [Member]	Jun. 30, 2013 Reconciling Eliminations [Member]	Jun. 30, 2012 Reconciling Eliminations [Member]	Dec. 31, 2012 Reconciling Eliminations [Member]	Jun. 30, 2013 Midstream Partnership [Member]	May 01, 2013 Midstream Partnership [Member]	Dec. 31, 2012 Midstream Partnership [Member]	Jun. 30, 2013 Midstream Partnership [Member] Midstream Investments [Member]	Jun. 30, 2013 CERC Remaining Interest in SESH [Member] Midstream Investments [Member]	Jun. 30, 2013 SESH [Member]	Dec. 31, 2012 SESH [Member]	Jun. 30, 2013 SESH [Member] Midstream Investments [Member]
Segment Reporting Information [Line Items]
Equity in earnings of unconsolidated affiliates	$ 37	$ 8	$ 42	$ 17																																											$ 33	$ 2
Revenues	1,235	846	3,088	2,396
Revenue from External Customers						524	360	1,567	1,209		622	302	1,210	822		41	[1]	88	133	[1]	170		48	[1]	96	178	[1]	195		0		0		0	0	0	0		0	0	0	0
Intersegment Revenue	0	0	0	0		5	6	13	11		6	6	15	11		13	[1]	37	53	[1]	82		7	[1]	8	18	[1]	14		0		0		0	0	0	0		(31)	(57)	(99)	(118)
Operating Income (Loss)	56	106	306	335		25	9	164	130		3	(4)	10	(3)		20	[1]	52	72	[1]	112		20	[1]	51	73	[1]	98		0	[2]	0		(12)	(2)	(13)	(2)		0	0	0	0
Assets	9,945		9,945		11,190	4,685		4,685		4,775	831		831		839	0			0			4,004	0			0			2,453	4,485	[2]	4,485	[2]	899		899		647	(955)		(955)		(1,528)
Investment in unconsolidated affiliates	$ 4,485		$ 4,485		$ 405																																							$ 4,285	$ 4,300	$ 0	$ 4,285		$ 200	$ 404	$ 200

[1] Results reflected in the three months ended June 30, 2013 represent only the month of April 2013. Results reflected in the six months ended June 30, 2013 represent only January 2013 through April 2013.

[2] Midstream Investments reported equity earnings of $33 million from Midstream Partnership and $2 million of equity earnings from CenterPoint Energy’s retained interest in SESH for the months of May and June 2013. Included in total assets of Midstream Investments as of June 30, 2013 is $4,285 million related to CenterPoint Energy’s investment in Midstream Partnership and $200 million related to CenterPoint Energy’s retained interest in SESH.