Employee Benefit Plans Pension and Postretirement Benefits (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Pension and Savings Plan
New percentage of eligible earnings used to determine retirement benefits (in hundredths)	5.00%
Pension Expense	$ 29		$ 32		$ 30
Non Qualified Pension Plan Benefit Expense	2		2		2
Maximum Percentage Of Employee Compensation Eligible For Contribution To Savings Plan	50.00%
Description Of Company Match Under Savings Plan	100% of the first 6% of each employee’s compensation contributed
Savings Plan Benefit Expense	19		18		17
Components of net periodic benefit cost
Service cost — benefits earned during the period	1		1		1
Interest cost on accumulated benefit obligation	5		5		6
Expected return on plan assets	(1)		(1)		(1)
Amortization of prior service cost	1		2		2
Amortization of net loss	2		3		1
Net postretirement benefit cost	8		10		9
Assumptions used to determine net postretirement benefit costs
Discount rate	3.90%		4.80%		5.20%
Expected return on plan assets	3.10%		3.10%		4.50%
Change in Plan Assets [Roll Forward]
Plan assets, beginning of year	24
Plan assets, end of year	26		24
Amounts Recognized in Balance Sheets
Other liabilities-benefit obligations	(102)		(122)
Actuarial Assumptions
Rate to which the cost trend rate is assumed to decline (ultimate trend rate)	5.50%
Annualized individual discount rates based on time period, minimum	6 months
Annualized individual discount rates based on time period, maximum	99 years
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Net current period other comprehensive income	6		6		(2)
Amounts recognized in accumulated other comprehensive loss
Unrecognized actuarial loss	9		20
Unrecognized prior service cost	1		2
Total recognized in accumulated other comprehensive loss	10		22
Less: deferred tax benefit (1)	(15)	[1]	(21)	[1]
Net amount recognized in accumulated other comprehensive (income) loss	(5)		1
Changes in plan assets and benefit obligations recognized in other comprehensive income
Net gain	11
Amortization of prior service cost	1
Total recognized in other comprehensive income	12
Total expense recognized in net periodic cost and other comprehensive income	4
Amounts that will be amortized from accumulated other comprehensive loss in next fiscal year
Unrecognized actuarial loss	0
Unrecognized prior service cost	0
Amounts in accumulated other comprehensive loss to be recognized as net periodic cost	0
Effect of a one-percentage point change in assumed healthcare cost trend rates
Effect of One Percentage Point Increase on Postretirement Benefit Obligation	2
Effect of One Percentage Point Increase on Total of Service and Interest Cost	0
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation	2
Effect of One Percentage Point Decrease on Total of Service and Interest Cost	0
Other Pension Plan, Postretirement or Supplemental Plans, Defined Benefit [Member]
Amounts reclassified from accumulated other comprehensive income: [Abstract]
Beginning Balance	(1)
Other comprehensive income before reclassifications (1)	10	[2]
Prior service cost (2)	1	[3]
Actuarial gains (2)	1	[3]
Total reclassifications from accumulated other comprehensive income	2
Tax expense	(6)
Net current period other comprehensive income	6
Ending Balance	5
Other Postretirement Benefit Plans, Defined Benefit [Member]
Change in Benefit Obligation [Roll Forward]
Accumulated benefit obligation, beginning of year	133		118
Service cost	1		1
Interest cost	5		5
Benefits paid	(13)		(13)
Participant contributions	4		4
Medicare reimbursement	2		2
Actuarial (gain) loss	(16)		16
Accumulated benefit obligation, end of year	116		133
Change in Plan Assets [Roll Forward]
Plan assets, beginning of year	24		22
Benefits paid	(13)		(13)
Employer contributions	9		9
Participant contributions	4		4
Actual investment return	2		2
Plan assets, end of year	26		24
Amounts Recognized in Balance Sheets
Current liabilities-other	(7)		(7)
Other liabilities-benefit obligations	(83)		(102)
Net liability, end of year	$ (90)		$ (109)
Actuarial Assumptions
Discount rate	4.75%		3.90%
Expected long-term return on assets	3.10%		3.10%
Prescription cost trend rate assumed for the next year	7.00%		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	2018		2017
Year that the prescription drug rate reaches the ultimate trend rate	2018		2017
Age Pre 65 [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Actuarial Assumptions
Healthcare cost trend rate assumed for the next year	7.00%		9.00%
Age Post 65 [Member] [Member] | Other Postretirement Benefit Plans, Defined Benefit [Member]
Actuarial Assumptions
Healthcare cost trend rate assumed for the next year	7.50%		9.00%

[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.

[2] Total other comprehensive income related to the re-measurement of pension, postretirement and other postemployment plans.

[3] These accumulated other comprehensive components are included in the computation of net periodic cost.