Employee Benefit Plans (Tables)

12 Months Ended

Dec. 31, 2016

Compensation and Retirement Disclosure [Abstract]

Schedule of Defined Benefit Plans Disclosures [Table Text Block]

CERC’s changes in accumulated comprehensive income (loss) related to postretirement and other postemployment plans are as follows:

	Year Ended December 31,
	2016			2015
	(in millions)
Beginning Balance	$	9		$	1
Other comprehensive income (loss) before reclassifications (1)	(10		)	13
Amounts reclassified from accumulated other comprehensive income:
Actuarial gains (2)	—			1
Tax benefit (expense)	4			(6		)
Net current period other comprehensive income (loss)	(6		)	8
Ending Balance	$	3		$	9

(1) Total other comprehensive income (loss) related to the remeasurement of pension, postretirement and other postemployment plans.

(2) These accumulated other comprehensive components are included in the computation of net periodic cost.

Amounts recognized in accumulated other comprehensive (income) loss consist of the following:

	December 31,
	2016			2015
	(in millions)
Unrecognized actuarial loss	$	5		$	3
Unrecognized prior service cost (credit)	7			(1		)
Total recognized in accumulated other comprehensive loss	12			2
Less: deferred tax benefit (1)	(15		)	(11		)
Net amount recognized in accumulated other comprehensive income	$	(3	)	$	(9	)

(1) 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.

The changes in plan assets and benefit obligations recognized in other comprehensive loss during 2016 are as follows:

	Postretirement Benefits
	(in millions)
Net loss	$	2
Amortization of prior service cost	8
Total recognized in other comprehensive loss	$	10

The following benefit payments are expected to be made by the postretirement benefit plan:

	Benefit Payments
	(in millions)
2017	$	5
2018	6
2019	7
2020	8
2021	8
2022-2026	43

As part of the investment strategy discussed above, CERC maintained the following asset allocation ranges for its postretirement benefit plan as of December 31, 2016:

U.S. equity	15–25%
International equity	2–12%
Fixed income	68–78%
Cash	0–2%

The net postretirement benefit cost includes the following components:

	Year Ended December 31,
	2016			2015			2014
	(in millions)
Service cost — benefits earned during the period	$	1		$	1		$	1
Interest cost on accumulated benefit obligation	4			5			5
Expected return on plan assets	(1		)	(1		)	(1		)
Amortization of prior service cost	—			1			1
Amortization of net loss	1			1			1
Curtailment (1)	(1		)	—			—
Net postretirement benefit cost	$	4		$	7		$	7

(1) Effective January 1, 2017, a change in retiree medical coverage for Medicare eligible post-65 retirees from self-insured to a Medicare Advantage Program, an insured benefit, was implemented. A curtailment gain was recognized in October 2016 related to this implementation.

CERC used the following assumptions to determine net postretirement benefit costs:

	Year Ended December 31,
	2016		2015		2014
Discount rate	4.35	%	3.90	%	4.75	%
Expected return on plan assets	3.95	%	4.05	%	3.10	%

Following are reconciliations of CERC’s beginning and ending balances of its postretirement benefit plan’s benefit obligation, plan assets and funded status for 2016 and 2015. The measurement dates for plan assets and obligations were December 31, 2016 and 2015.

	December 31,
	2016			2015
	(in millions, except for actuarial assumptions)
Change in Benefit Obligation
Accumulated benefit obligation, beginning of year	$	101		$	126
Service cost	1			1
Interest cost	4			5
Benefits paid	(13		)	(12		)
Participant contributions	5			4
Medicare reimbursement	1			1
Plan amendment (1)	10			(5		)
Actuarial (gain) loss	6			(19		)
Accumulated benefit obligation, end of year	$	115		$	101
Change in Plan Assets
Plan assets, beginning of year	$	25		$	26
Benefits paid	(13		)	(12		)
Employer contributions	7			7
Participant contributions	5			4
Actual investment return	1			—
Plan assets, end of year	$	25		$	25
Amounts Recognized in Balance Sheets
Current liabilities-other	$	(4	)	$	(6	)
Other liabilities-benefit obligations	(86		)	(70		)
Net liability, end of year	$	(90	)	$	(76	)
Actuarial Assumptions
Discount rate	4.15		%	4.35		%
Expected long-term return on assets	3.60		%	3.95		%
Healthcare cost trend rate assumed for the next year - Pre 65	5.75		%	6.00		%
Healthcare cost trend rate assumed for the next year - Post 65	10.65		%	5.50		%
Prescription cost trend rate assumed for the next year	10.75		%	11.00		%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)	4.50		%	5.00		%
Year that the healthcare rate reaches the ultimate trend rate	2024			2024
Year that the prescription drug rate reaches the ultimate trend rate	2024			2024

(1) The postretirement plan was amended in 2016 to change the retiree medicalcoverage for Medicare eligible post-65 retirees from self-insured to a Medicare Advantage Program, an insured benefit which became effective January 1, 2017.

Defined Benefit Plan Schedule Of Effect Of One Percentage 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 CERC’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	$	4	$	4
Effect on the total of service and interest cost	—		—

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

The fair values of CERC’s postretirement plan assets at December 31, 2016 and 2015, by asset category are as follows:

	Fair Value Measurements as of December 31, 2016
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Mutual funds (1)	$	25	$	—	$	—	$	25
Total	$	25	$	—	$	—	$	25

(1) 73% of the amount invested in mutual funds was in fixed income securities; 20% was in U.S. equities and 7% was in international equities.

	Fair Value Measurements as of December 31, 2015
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Total
Mutual funds (1)	$	25	$	—	$	—	$	25
Total	$	25	$	—	$	—	$	25

(1) 70% of the amount invested in mutual funds was in fixed income securities; 23% was in U.S. equities and 7% was in international equities.