Credit Risk (Narrative) (Details) $ in Millions	12 Months Ended
Dec. 31, 2015 USD ($) customer	Dec. 31, 2014 USD ($)
Concentration Risk [Line Items]
Gross credit exposure	$ 149
Additional collateral to be posted if the credit-related contingent features were triggered	12	$ 20
Collateral already posted	0	1
Aggregate fair value of derivative instruments in a liability position and not fully collateralized with cash	$ 49	$ 49
Investment Grade Counterparties \| Investment Grade
Concentration Risk [Line Items]
Concentration of credit risk	79.00%
CounterpartyA
Concentration Risk [Line Items]
Amount of exposure	$ 31
Customer Concentration Risk \| Sales Revenue, Net \| DTI
Concentration Risk [Line Items]
Concentration of credit risk	94.00%
Number of customers \| customer	266
Customer Concentration Risk \| Sales Revenue, Net \| DTI \| Ten Largest Customers
Concentration Risk [Line Items]
Concentration of credit risk	42.00%
Number of customers \| customer	10
Customer Concentration Risk \| Sales Revenue, Net \| DTI \| Thirty Largest Customers
Concentration Risk [Line Items]
Concentration of credit risk	72.00%
Number of customers \| customer	30
Customer Concentration Risk \| Sales Revenue, Net \| East Ohio
Concentration Risk [Line Items]
Concentration of credit risk	98.00%

Concentration Risk, Credit Risk, Financial Instrument, Maximum Exposure for Single Counter Party

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Concentration Risk, Number of Customers Provided Service

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The aggregate fair value of additional assets that would be required to be posted as collateral for derivative instruments with credit-risk-related contingent features if the credit-risk-related contingent features were triggered at the end of the reporting period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (e)
-URI http://asc.fasb.org/extlink&oid=56946850&loc=SL5624258-113959

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The aggregate fair value of assets that are already posted, at the end of the reporting period, as collateral for derivative instruments with credit-risk-related contingent features.

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Maximum amount of loss due to credit risk that, based on the gross fair value of the financial instrument, the entity would incur if parties to the financial instruments that make up the concentration failed completely to perform according to the terms of the contracts and the collateral or other security, if any, for the amount due proved to be of no value to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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-SubTopic 10
-Section 50
-Paragraph 21
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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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No definition available.

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For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

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-Publisher FASB
-Name Accounting Standards Codification
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The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

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