Employee Benefit Plans Pension and Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	0 Months Ended	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
New percentage of eligible earnings used to determine retirement benefits (in hundredths)	5.00%		5.00%
Recognized pension expense			$ 26us-gaap_PensionExpense	$ 25us-gaap_PensionExpense	$ 30us-gaap_PensionExpense
Non Qualified Pension Plan Expense			1	1	1
Deferred Compensation Arrangement with Individual, Compensation Expense			1	1	1
Maximum Percentage Of Employee Compensation Eligible For Contribution To Savings Plan			50.00%
Description Of Company Match Under Savings Plan			100.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay			6.00%
Defined Contribution Plan, Cost Recognized			13	13	12
Components of net periodic costs [Abstract]
Service cost - benefits earned during the period			1us-gaap_DefinedBenefitPlanServiceCost	1us-gaap_DefinedBenefitPlanServiceCost	0us-gaap_DefinedBenefitPlanServiceCost
Interest cost on accumulated benefit obligation			14us-gaap_DefinedBenefitPlanInterestCost	13us-gaap_DefinedBenefitPlanInterestCost	16us-gaap_DefinedBenefitPlanInterestCost
Expected return on plan assets			(6)	(7)	(7)
Amortization of transition obligation			4	6	6
Amortization of prior service credit			(2)	(1)	0
Amortization of loss			1	4	3
Benefit enhancement			0cehe_DefinedBenefitPlanEnhancements	0cehe_DefinedBenefitPlanEnhancements	1cehe_DefinedBenefitPlanEnhancements
Net postretirement benefit cost			12	16	19
Assumptions used to determine net periodic benefit (income) cost [Abstract]
Discount rate (in hundredths)			4.75%	3.90%	4.80%
Expected return on plan assets (in hundredths)	5.45%	6.00%	6.00%	6.00%	6.00%
Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation, beginning of year	347	311	311	351
Service cost - benefits earned during the period			1us-gaap_DefinedBenefitPlanServiceCost	1us-gaap_DefinedBenefitPlanServiceCost	0us-gaap_DefinedBenefitPlanServiceCost
Interest cost on accumulated benefit obligation			14us-gaap_DefinedBenefitPlanInterestCost	13us-gaap_DefinedBenefitPlanInterestCost	16us-gaap_DefinedBenefitPlanInterestCost
Benefits paid			(18)us-gaap_DefinedBenefitPlanBenefitsPaid	(19)us-gaap_DefinedBenefitPlanBenefitsPaid
Participant contributions			3	3
Medicare drug reimbursement			1	1
Actuarial (gain) loss			35	(39)
Accumulated benefit obligation, end of year	347	311	347	311	351
Change in Plan Assets [Roll Forward]
Plan assets, beginning of year	115	114	114	115
Benefits paid			(18)us-gaap_DefinedBenefitPlanBenefitsPaid	(19)us-gaap_DefinedBenefitPlanBenefitsPaid
Employer contributions			9	9
Participant contributions			3	3
Actual investment return			7	6
Plan assets, end of year	115	114	115	114	115
Amounts Recognized in Balance Sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	(260)	(227)	(260)	(227)
Net liability, end of year	(232)	(197)	(232)	(197)
Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	3.90%	4.75%	3.90%	4.75%
Expected return on plan assets (in hundredths)	5.45%	6.00%	6.00%	6.00%	6.00%
Prescription drug cost trend rate assumed for the next year			6.50%	7.00%
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)			5.00%	5.50%
Year that the healthcare rate reaches the ultimate trend rate	2024	2018	2024	2018
Year that the prescription drug rate reaches the ultimate trend rate			2024	2018
Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Effect of One Percentage Point Increase on Postretirement Benefit Obligation			13
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation			11
Effect of One Percentage Point Increase on Total Service and Interest Cost			1
Effect of One Percentage Point Decrease on Total Service and Interest Cost			0
Annualized individual discount rates based on time period, minimum			6 months
Annualized individual discount rates based on time period, maximum			99 years
Other Postretirement Benefit Plans, Defined Benefit [Member]
Amounts Recognized in Balance Sheets [Abstract]
Pension and Other Postretirement Defined Benefit Plans, Liabilities, Noncurrent	$ (232)	$ (197)	$ (232)	$ (197)
Age Pre 65 [Member]
Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for the next year			7.25%	7.00%
Age Post 65 [Member] [Member]
Assumed Health Care Cost Trend Rates [Abstract]
Healthcare cost trend rate assumed for the next year			8.50%	7.50%

Annualized individual discount rates based on time period, maximum

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The amount of increase or decrease to net periodic benefit cost as a result of plan enhancements.

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The assumed prescription drug cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of prescription drugs currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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The increased percentage of earnings, effective January 1, 2009, used in the cash balance formula to determine a participant's retirement benefit.

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Year the ultimate prescription drug rate is expected to be reached in CCYY format

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Benefit expense recorded during the period related to non-qualified pension arrangements

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The compensation expense recognized during the period pertaining to the deferred compensation arrangement.

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The difference between fair value of plan assets at the end of the period and the fair value at the beginning of the period, adjusted for contributions and payments of benefits during the period, and after adjusting for taxes and other expenses, as applicable.

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Amount of gain (loss) related to change in benefit obligation resulting from changes in actuarial assumptions, for example, but not limited to, interest, mortality, employee turnover, salary, and temporary deviation from the substantive plan.

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The amount of gains or losses recognized in net periodic benefit cost.

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The amount of the prior service cost or credit recognized in net periodic benefit cost relating to benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation.

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The amount of the transition obligation or asset recognized in net periodic benefit cost.

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The interest rate used to adjust for the time value of money for the plan.

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The interest rate used to adjust for the time value of money.

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An assumption as to the rate of return on plan assets reflecting the average rate of earnings expected on the funds invested or to be invested to provide for the benefits included in the benefit obligation.

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1) For defined benefit pension plans, the benefit obligation is the projected benefit obligation, which is the actuarial present value as of a date of all benefits attributed by the pension benefit formula to employee service rendered prior to that date. 2) For other postretirement defined benefit plans, the benefit obligation is the accumulated postretirement benefit obligation, which is the actuarial present value of benefits attributed to employee service rendered to a particular date.

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-Glossary Accumulated Postretirement Benefit Obligation

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The amount of payments made for which participants are entitled under a pension plan, including pension benefits, death benefits, and benefits due on termination of employment. Also includes payments made under a postretirement benefit plan, including prescription drug benefits, health care benefits, life insurance benefits, and legal, educational and advisory services. This item represents a periodic decrease to the plan obligations and a decrease to plan assets.

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The increase in the fair value of plan assets from contributions made by the employer.

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The amount of contributions made by plan participants. This item represents a periodic increase to the plan obligation and an increase to plan assets.

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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Amount of effect of a one-percentage-point decrease in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the accumulated postretirement benefit obligation for health care benefits.

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The effect of a one-percentage-point increase in the assumed health care cost trend rates on the aggregate of the service and interest cost components of net periodic postretirement health care benefit costs.

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An amount calculated as a basis for determining the extent of delayed recognition of the effects of changes in the fair value of assets. The expected return on plan assets is determined based on the expected long-term rate of return on plan assets and the market-related value of plan assets.

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Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

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Amount of the period's gross receipts received from the prescription drug subsidy, which is to be used in the roll forward of the accumulated postretirement benefit obligation of an applicable postretirement benefit plan.

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The assumed health care cost trend rate for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

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The increase in a defined benefit pension plan's projected benefit obligation or a defined benefit postretirement plan's accumulated postretirement benefit obligation due to the passage of time.

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The total amount of net periodic benefit cost for defined benefit plans for the period. Periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss), prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments.

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The actuarial present value of benefits attributed by the pension benefit formula to services rendered by employees during the period. The portion of the expected postretirement benefit obligation attributed to employee service during the period. The service cost component is a portion of the benefit obligation and is unaffected by the funded status of the plan.

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The ultimate trend rate for health care costs.

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Year the ultimate health care cost trend rate is expected to be reached, in CCYY format.

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The amount of the cost recognized during the period for defined contribution plans.

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Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

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No definition available.

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Percentage employer matches of the employee's percentage contribution matched.

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Maximum percentage of employee gross pay the employee may contribute to a defined contribution plan.

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This represents the entire liability recognized in the balance sheet that is associated with the defined benefit plans.

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This represents the noncurrent liability for underfunded plans recognized in the balance sheet that is associated with the defined benefit pension plans and other postretirement defined benefit plans.

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The amount of pension benefit costs recognized during the period for (1) defined benefit plans and (2) defined contribution plans. For defined benefit plans, pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. For defined contribution plans, the pension expense generally equals the firm's contribution to employees' accounts (if the firm contributes) during the period.

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