Derivative Instruments and Hedging Activities (Commodity Derivatives) (Details)	12 Months Ended
Dec. 31, 2014 MWh
Power MWh \| Commodity Contract
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	5,000,000
Derivative average remaining maturity	2 years
Coal Metric Tons
Derivative [Line Items]
Derivative, Nonmonetary Notional Amount	1,000,000
Derivative average remaining maturity	1 year

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 12

-Section 13

-Sentence Column B

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant