Stock-Based Incentive Compensation Plans and Employee Benefit Plans Pension and Postretirement Benefits (Details) - USD ($) $ in Millions						12 Months Ended
		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Pension and Postretirement Benefits [Abstract]
Percentage of eligible earnings used to determine retirement benefits (in hundredths)		5.00%				5.00%
Percent vested						100.00%
Pension plan minimum vesting period (in years)						3 years
Amounts recognized in balance sheets
Other liabilities-benefit obligations		$ (796)		$ (785)		$ (796)		$ (785)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss	[1]					(6)		(7)
Prior service cost (2)	[1]					(1)		(1)
Pension Plan [Member]
Components of net periodic costs [Abstract]
Service cost (1)	[2]					37		36		$ 38
Interest cost (2)	[3]					79		89		93
Expected return on plan assets (2)	[3]					(107)		(97)		(101)
Amortization of prior service cost (credit)	[3]					9		9		9
Amortization of net loss (2)	[3]					43		58		63
Net periodic cost (credit)						$ 61		$ 95		$ 102
Assumptions used to determine net periodic benefit (income) cost
Discount rate						3.65%		4.15%		4.40%
Expected return on plan assets						6.00%	[4]	6.00%	[4]	6.25%
Rate of increase in compensation levels						4.45%		4.50%		4.15%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year						$ 2,225		$ 2,197
Service cost (1)	[2]					37		36		$ 38
Interest cost (2)	[3]					79		89		93
Benefits paid						(201)		(168)
Actuarial (gain) loss (1)	[5]					(127)		71
Benefit obligation, end of year		2,013		2,225		2,013		2,225		2,197
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						1,801		1,656
Employer contributions						69		48
Benefits paid						(201)		(168)
Actual investment return						(153)		265
Fair value of plan assets, end of year		1,516		1,801		1,516		1,801		$ 1,656
Funded status of plan
Funded status, end of year		(497)		(424)		(497)		(424)
Amounts recognized in balance sheets
Current liabilities-other		(7)		(7)		(7)		(7)
Other liabilities-benefit obligations		(490)		(417)		(490)		(417)
Net liability, end of year		$ (497)		$ (424)		$ (497)		$ (424)
Discount rate (2)		4.35%	[6]	3.65%	[6]	4.35%	[6]	3.65%	[6]	4.15%
Expected return on plan assets (3)						6.00%	[4]	6.00%	[4]	6.25%
Rate of increase in compensation levels		4.60%		4.45%		4.60%		4.45%
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Weighted-Average Interest Crediting Rate		3.75%		3.75%		3.75%		3.75%
Annualized individual discount rates based on time period, minimum						6 months
Annualized individual discount rates based on time period, maximum						99 years
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)		$ 109		$ 94		$ 109		$ 94
Unrecognized prior service cost		1		1		1		1
Deferred Tax Benefit On Accumulated Other Comprehensive Income	[7]	0		0		0		0
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		110		95		110		95
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)						22
Amortization of net loss						(6)
Prior service cost (2)						(1)
Total recognized in comprehensive income						15
Total expense recognized in net periodic cost and other comprehensive income						76
Pension benefits that have accumulated benefit obligations in excess of plan assets
Accumulated benefit obligation		1,930		2,090		1,930		2,090
Projected benefit obligation		1,952		2,151		1,952		2,151
Fair value of plan assets		1,516		1,801		1,516		1,801
Accumulated benefit obligation for all defined benefit pension plans		$ 1,991		$ 2,164		1,991		2,164
Postretirement Benefits [Member]
Components of net periodic costs [Abstract]
Service cost (1)	[8]					2		2		$ 2
Interest cost (2)	[9]					13		16		16
Expected return on plan assets (2)	[9]					(5)		(5)		(6)
Amortization of prior service cost (credit)	[9]					(5)		(5)		(3)
Amortization of net loss (2)	[9]					0		0		1
Curtailment (1)	[10]					0		0		(5)
Net periodic cost (credit)						$ 5		$ 8		$ 5
Assumptions used to determine net periodic benefit (income) cost
Discount rate						3.60%		4.15%		4.35%
Expected return on plan assets		4.60%	[11]	4.55%	[11]	4.55%		4.50%		4.80%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year						$ 386		$ 383
Service cost (1)	[8]					2		2		$ 2
Interest cost (2)	[9]					13		16		16
Participant contributions						7		7
Benefits paid						(25)		(26)
Actuarial (gain) loss (1)	[12]					(52)		4
Benefit obligation, end of year		$ 331		$ 386		331		386		383
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						120		113
Employer contributions						14		16
Participant contributions						7		7
Benefits paid						(25)		(26)
Actual investment return						(2)		10
Fair value of plan assets, end of year		114		120		114		120		$ 113
Funded status of plan
Funded status, end of year		(217)		(266)		(217)		(266)
Amounts recognized in balance sheets
Current liabilities-other		(6)		(6)		(6)		(6)
Other liabilities-benefit obligations		(211)		(260)		(211)		(260)
Net liability, end of year		$ (217)		$ (266)		$ (217)		$ (266)
Discount rate (2)	[13]	4.35%		3.60%		4.35%		3.60%
Expected return on plan assets (3)		4.60%	[11]	4.55%	[11]	4.55%		4.50%		4.80%
Prescription drug cost trend rate assumed for the next year - Pre-65						9.20%		9.85%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)		4.50%		4.50%		4.50%		4.50%
Annualized individual discount rates based on time period, minimum						6 months
Annualized individual discount rates based on time period, maximum						99 years
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)		$ (7)		$ (8)		$ (7)		$ (8)
Unrecognized prior service cost		5		6		5		6
Deferred Tax Benefit On Accumulated Other Comprehensive Income	[7]	0		0		0		0
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		(2)		(2)		(2)		(2)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)						0
Amortization of net loss						0
Prior service cost (2)						0
Total recognized in comprehensive income						0
Total expense recognized in net periodic cost and other comprehensive income						5
Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions						9
Pension benefits that have accumulated benefit obligations in excess of plan assets
Accumulated benefit obligation		61		74		61		74
Projected benefit obligation		61		74		61		74
Fair value of plan assets		0		0		0		0
U.S. Equity [Member] | Pension Plan [Member]
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						76
Fair value of plan assets, end of year		60		76		60		76
Cash and Cash Equivalents [Member] | Pension Plan [Member]
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						18
Fair value of plan assets, end of year		$ 19		$ 18		$ 19		$ 18
Minimum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		5.95%		6.15%		5.95%		6.15%
Year that the cost trend rates reach the ultimate trend rate						2026		2026
Minimum [Member] | U.S. Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		12.00%				12.00%
Minimum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		13.00%				13.00%
Minimum [Member] | International Developed Market Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		7.00%				7.00%
Minimum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		3.00%				3.00%
Minimum [Member] | Emerging Market Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		5.00%				5.00%
Minimum [Member] | Fixed Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		55.00%				55.00%
Minimum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		69.00%				69.00%
Minimum [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		0.00%				0.00%
Minimum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		0.00%				0.00%
Maximum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		28.60%		23.85%		28.60%		23.85%
Year that the cost trend rates reach the ultimate trend rate						2027		2024
Maximum [Member] | U.S. Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		28.00%				28.00%
Maximum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		23.00%				23.00%
Maximum [Member] | International Developed Market Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		17.00%				17.00%
Maximum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		13.00%				13.00%
Maximum [Member] | Emerging Market Equity [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		11.00%				11.00%
Maximum [Member] | Fixed Income [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		65.00%				65.00%
Maximum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		79.00%				79.00%
Maximum [Member] | Cash and Cash Equivalents [Member] | Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%				2.00%
Maximum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%				2.00%
Parent Company [Member] | Postretirement Benefits [Member]
Components of net periodic costs [Abstract]
Curtailment (1)										$ (2)
Houston Electric [Member]
Amounts recognized in balance sheets
Other liabilities-benefit obligations		$ (91)		$ (146)		$ (91)		$ (146)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss	[1]					0		0
Prior service cost (2)	[1]					0		0
Houston Electric [Member] | Postretirement Benefits [Member]
Components of net periodic costs [Abstract]
Service cost (1)	[8]					0		1		1
Interest cost (2)	[9]					8		9		10
Expected return on plan assets (2)	[9]					(4)		(4)		(5)
Amortization of prior service cost (credit)	[9]					(5)		(6)		(4)
Amortization of net loss (2)	[9]					0		0		1
Curtailment (1)	[10]					0		0		(4)
Net periodic cost (credit)						$ (1)		$ 0		$ (1)
Assumptions used to determine net periodic benefit (income) cost
Discount rate						3.60%		4.15%		4.35%
Expected return on plan assets		4.70%	[11]	4.75%	[11]	4.75%		4.75%		5.00%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year						$ 225		$ 217
Service cost (1)	[8]					0		1		$ 1
Interest cost (2)	[9]					8		9		10
Participant contributions						2		2
Benefits paid						(13)		(14)
Actuarial (gain) loss (1)	[12]					(56)		10
Benefit obligation, end of year		$ 166		$ 225		166		225		217
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						93		88
Employer contributions						9		10
Participant contributions						2		2
Benefits paid						(13)		(14)
Actual investment return						(2)		7
Fair value of plan assets, end of year		89		93		89		93		$ 88
Funded status of plan
Funded status, end of year		(77)		(132)		(77)		(132)
Amounts recognized in balance sheets
Current liabilities-other		0		0		0		0
Other liabilities-benefit obligations		(77)		(132)		(77)		(132)
Net liability, end of year		$ (77)		$ (132)		$ (77)		$ (132)
Discount rate (2)	[13]	4.35%		3.60%		4.35%		3.60%
Expected return on plan assets (3)		4.70%	[11]	4.75%	[11]	4.75%		4.75%		5.00%
Prescription drug cost trend rate assumed for the next year - Pre-65						9.20%		9.85%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)		4.50%		4.50%		4.50%		4.50%
Annualized individual discount rates based on time period, minimum						6 months
Annualized individual discount rates based on time period, maximum						99 years
Houston Electric [Member] | Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions						$ 0
Houston Electric [Member] | Minimum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		5.95%		6.15%		5.95%		6.15%
Year that the cost trend rates reach the ultimate trend rate						2026		2026
Houston Electric [Member] | Minimum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		13.00%				13.00%
Houston Electric [Member] | Minimum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		3.00%				3.00%
Houston Electric [Member] | Minimum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		69.00%				69.00%
Houston Electric [Member] | Minimum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		0.00%				0.00%
Houston Electric [Member] | Maximum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		28.60%		23.85%		28.60%		23.85%
Year that the cost trend rates reach the ultimate trend rate						2027		2024
Houston Electric [Member] | Maximum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		23.00%				23.00%
Houston Electric [Member] | Maximum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		13.00%				13.00%
Houston Electric [Member] | Maximum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		79.00%				79.00%
Houston Electric [Member] | Maximum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%				2.00%
CERC Corp [Member]
Amounts recognized in balance sheets
Other liabilities-benefit obligations		$ (93)		$ (97)		$ (93)		$ (97)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Amortization of net loss	[1]					0		0
Prior service cost (2)	[1]					(1)		(1)
CERC Corp [Member] | Postretirement Benefits [Member]
Components of net periodic costs [Abstract]
Service cost (1)	[8]					1		1		$ 1
Interest cost (2)	[9]					4		5		4
Expected return on plan assets (2)	[9]					(1)		(1)		(1)
Amortization of prior service cost (credit)	[9]					1		1		0
Amortization of net loss (2)	[9]					0		0		1
Curtailment (1)	[10]					0		0		(1)
Net periodic cost (credit)						$ 5		$ 6		$ 4
Assumptions used to determine net periodic benefit (income) cost
Discount rate						3.60%		4.15%		4.35%
Expected return on plan assets		4.15%	[11]	3.85%	[11]	3.85%		3.60%		3.95%
Change in benefit obligation [Roll Forward]
Benefit obligation, beginning of year						$ 109		$ 115
Service cost (1)	[8]					1		1		$ 1
Interest cost (2)	[9]					4		5		4
Participant contributions						4		3
Benefits paid						(9)		(9)
Actuarial (gain) loss (1)	[12]					1		(6)
Benefit obligation, end of year		$ 110		$ 109		110		109		115
Change in plan assets [Rollforward]
Fair value of plan assets, beginning of year						26		25
Employer contributions						4		5
Participant contributions						4		3
Benefits paid						(9)		(9)
Actual investment return						0		2
Fair value of plan assets, end of year		25		26		25		26		$ 25
Funded status of plan
Funded status, end of year		(85)		(83)		(85)		(83)
Amounts recognized in balance sheets
Current liabilities-other		(3)		(4)		(3)		(4)
Other liabilities-benefit obligations		(82)		(79)		(82)		(79)
Net liability, end of year		$ (85)		$ (83)		$ (85)		$ (83)
Discount rate (2)	[13]	4.35%		3.60%		4.35%		3.60%
Expected return on plan assets (3)		4.15%	[11]	3.85%	[11]	3.85%		3.60%		3.95%
Prescription drug cost trend rate assumed for the next year - Pre-65						9.20%		9.85%
Rate to which the cost trend rate is assumed to decline (the ultimate trend rate)		4.50%		4.50%		4.50%		4.50%
Annualized individual discount rates based on time period, minimum						6 months
Annualized individual discount rates based on time period, maximum						99 years
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss (gain)		$ (3)		$ (2)		$ (3)		$ (2)
Unrecognized prior service cost		5		6		5		6
Deferred Tax Benefit On Accumulated Other Comprehensive Income	[7]	(9)		(11)		(9)		(11)
Accumulated Other Comprehensive Income (Loss), Defined Benefit Plan, Gain (Loss), after Tax		$ (7)		$ (7)		(7)		$ (7)
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net loss (gain)						(1)
Amortization of net loss						0
Prior service cost (2)						(1)
Total recognized in comprehensive income						(2)
Total expense recognized in net periodic cost and other comprehensive income						3
CERC Corp [Member] | Non-qualified Pension Plan [Member]
Change in plan assets [Rollforward]
Employer contributions						$ 0
CERC Corp [Member] | Minimum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		5.95%		6.15%		5.95%		6.15%
Year that the cost trend rates reach the ultimate trend rate						2026		2026
CERC Corp [Member] | Minimum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		15.00%				15.00%
CERC Corp [Member] | Minimum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%				2.00%
CERC Corp [Member] | Minimum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		68.00%				68.00%
CERC Corp [Member] | Minimum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		0.00%				0.00%
CERC Corp [Member] | Maximum [Member] | Postretirement Benefits [Member]
Amounts recognized in balance sheets
Health care cost trend rate assumed for the next year		28.60%		23.85%		28.60%		23.85%
Year that the cost trend rates reach the ultimate trend rate						2027		2024
CERC Corp [Member] | Maximum [Member] | U.S. Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		25.00%				25.00%
CERC Corp [Member] | Maximum [Member] | International Developed Market Equity [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		12.00%				12.00%
CERC Corp [Member] | Maximum [Member] | Fixed Income [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		78.00%				78.00%
CERC Corp [Member] | Maximum [Member] | Cash and Cash Equivalents [Member] | Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Plan Assets, Target Allocation, Percentage		2.00%				2.00%
IBEW Local Union 66 [Member] | Houston Electric [Member] | Postretirement Benefits [Member]
Components of net periodic costs [Abstract]
Curtailment (1)										$ (3)

[1] Amounts are included in the computation of net periodic cost and are reflected in Other, net in each of the Registrants’ respective Statements of Consolidated Income.

[2] Amounts presented in the table above are included in Operation and maintenance expense in CenterPoint Energy’s Statements of Consolidated Income, net of regulatory deferrals and amounts capitalized. See Note 2(r).

[3] Amounts presented in the table above are included in Other, net in CenterPoint Energy’s Statements of Consolidated Income, net of regulatory deferrals. See Note 2(r).

[4] The expected rate of return assumption was developed using the targeted asset allocation of CenterPoint Energy’s plans and the expected return for each asset class.

[5] Significant sources of gain for 2018 include the increase in discount rate from 3.65% to 4.35% and the mortality projection scale change from MP2017 to MP2018. For 2017, the significant source of loss was the decrease in the discount rate from 4.15% to 3.65%.

[6] The discount rate assumption was determined by matching the projected cash flows of CenterPoint Energy’s plans against a hypothetical yield curve of high-quality corporate bonds represented by a series of annualized individual discount rates from one-half to 99 years.

[7] CenterPoint Energy’s and CERC’s postretirement benefit obligation is reduced by the impact of previously non-taxable government subsidies under the Medicare Prescription Drug Act. Because the subsidies were non-taxable, the temporary difference used in measuring the deferred tax impact was determined on the unrecognized losses excluding such subsidies.

[8] Amounts presented in the table above are included in Operation and maintenance expense in CenterPoint Energy’s Statements of Consolidated Income, net of regulatory deferrals and amounts capitalized. See Note 2(r).

[9] Amounts presented in the table above are included in Other, net in each of the Registrants’ respective Statements of Consolidated Income, net of regulatory deferrals. See Note 2(r).

[10] A curtailment gain or loss is required when the expected future services of a significant number of current employees are reduced or eliminated for the accrual of benefits. During 2016, postretirement healthcare benefits were amended resulting in a net curtailment gain of $5 million. In May 2016, Houston Electric entered into a renegotiated collective bargaining agreement with the IBEW Local Union 66 that provides that for Houston Electric bargaining unit employees covered under the agreement who retire on or after January 1, 2017, retiree medical and prescription drug coverage will be provided exclusively through the NECA/IBEW Family Medical Care Plan in exchange for the payment of monthly premiums as determined under the agreement. As a result, the accrued postretirement benefits related to such future CenterPoint Energy and Houston Electric union retirees were eliminated. Houston Electric recognized a curtailment gain of $3 million as an accelerated recognition of the prior service credit that would otherwise be recognized in future periods for the postretirement plan. CenterPoint Energy also recognized an additional curtailment gain of $2 million in October 2016 related to other amendments in the postretirement plan.

[11] The expected rate of return assumption was developed using the targeted asset allocation of the plans and the expected return for each asset class.

[12] Significant sources of gain for 2018 include the increase in the discount rate from 3.60% to 4.35%, favorable benefit claims experience and cost trend rates in addition to the change in mortality projection scale from MP2017 to MP2018.

[13] The discount rate assumption was determined by matching the projected cash flows of the plans against a hypothetical yield curve of high-quality corporate bonds represented by a series of annualized individual discount rates from one-half to 99 years.