Risk Management and Hedging Activities Risk Management and Hedging Activities - Derivative Contract Volumes (Details) (Commodity Contract [Member])	Dec. 31, 2014 MWh	Dec. 31, 2013 MWh
Electricity sales, in megawatt hours [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount	(1,000,000)	(1,000,000)
Natural gas purchases, in decatherms [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount	113,000,000	120,000,000
Fuel oil purchases, in gallons [Member]
Notional Amounts of Outstanding Derivative Positions [Line Items]
Derivative, Nonmonetary Notional Amount	3,000,000	15,000,000