Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2012

Compensation and Retirement Disclosure [Abstract]

Schedule of Defined Benefit Plans Disclosures [Table Text Block]

Following are reconciliations of CenterPoint Houston’s beginning and ending balances of its postretirement benefit plan’s benefit obligation, plan assets and funded status for 2011 and 2012.  The measurement dates for plan assets and obligations were December 31, 2011 and 2012.

	Year Ended December 31,
	2011			2012
	(in millions)
Change in Benefit Obligation
Accumulated benefit obligation, beginning of year	$	306		$	335
Interest cost	16			16
Benefits paid	(23		)	(21		)
Participant contributions	2			2
Medicare drug reimbursement	3			2
Actuarial loss	31			17
Accumulated benefit obligation, end of year	$	335		$	351
Change in Plan Assets
Plan assets, beginning of year	$	122		$	116
Benefits paid	(23		)	(21		)
Employer contributions	9			9
Participant contributions	2			2
Actual investment return	6			9
Plan assets, end of year	$	116		$	115
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations	$	(219	)	$	(236	)
Net liability, end of year	$	(219	)	$	(236	)
Actuarial Assumptions
Discount rate	4.80		%	3.90		%
Expected long-term return on assets	6.00		%	6.00		%
Healthcare cost trend rate assumed for the next year	8.00		%	9.00		%
Prescription drug cost trend rate assumed for the next year	8.00		%	9.00		%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)	5.50		%	5.50		%
Year that the healthcare rate reaches the ultimate trend rate	2017			2017
Year that the prescription drug rate reaches the ultimate trend rate	2017			2017

CenterPoint Houston is required to fund a portion of its obligations in accordance with rate orders. The net postretirement benefit cost includes the following components:

	Year Ended December 31,
	2010			2011			2012
	(in millions)
Interest cost on accumulated benefit obligation	$	16		$	16		$	16
Expected return on plan assets	(9		)	(9		)	(7		)
Amortization of transition obligation	6			6			6
Amortization of loss	—			1			3
Benefit enhancement	—			1			1
Net postretirement benefit cost	$	13		$	15		$	19

CenterPoint Houston used the following assumptions to determine net postretirement benefit costs:

	Year Ended December 31,
	2010		2011		2012
Discount rate	5.70	%	5.20	%	4.80	%
Expected return on plan assets	7.50	%	7.50	%	6.00	%

As part of the investment strategy discussed above, CenterPoint Houston has adopted and maintained the following asset allocation ranges for its postretirement benefit plans:

U.S. equity	13-23%
International equity	3-13%
Fixed income	68-78%
Cash	0-2%

CenterPoint Houston expects to contribute $7 million to its postretirement benefits plan in 2013. The following benefit payments are expected to be paid by the postretirement benefit plan (in millions): 

	Postretirement Benefit Plan
	Benefit Payments		Medicare Subsidy Receipts
2013	$	21	$	(2	)
2014	22		(2		)
2015	23		(2		)
2016	24		(3		)
2017	25		(3		)
2018-2022	136		(16		)

Schedule of a one-percent point change In Assumed Health Care Cost Trend Rates [Table Text Block]

Assumed healthcare cost trend rates have a significant effect on the reported amounts for CenterPoint Houston’s postretirement benefit plans. A 1% change in the assumed healthcare cost trend rate would have the following effects:

	1% Increase		1% Decrease
	(in millions)
Effect on the postretirement benefit obligation	$	13	$	(11	)
Effect on total of service and interest cost	—		—

Schedule Of Fair Value Of Financial Assets For Pension And Postretirement Benefits [Text Block]

The following tables present by level, within the fair value hierarchy, CenterPoint Houston’s postretirement plan assets as of December 31, 2011 and 2012, by asset category as follows:

	Fair Value Measurements at December 31, 2011 (in millions)
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Mutual funds (1)	$	116	$	116	$	—	$	—
Total	$	116	$	116	$	—	$	—

(1) 74% of the amount invested in mutual funds is in fixed income securities; 18% is in U.S. equities and 8% is in international equities.

	Fair Value Measurements at December 31, 2012 (in millions)
	Total		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
Mutual funds (1)	$	115	$	115	$	—	$	—
Total	$	115	$	115	$	—	$	—

(1) 74% of the amount invested in mutual funds is in fixed income securities; 18% is in U.S. equities and 8% is in international equities.