Fair Value of Financial Assets and Liabilities, Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014 MWh		Dec. 31, 2013 MWh
Interest Rate Swap
Interest Rate Derivatives [Abstract]
Amount of accumulated other comprehensive losses related to interest rate derivatives expected to be reclassified into earnings within the next twelve months	$ (0.2)
Electric Commodity
Gross Notional Amounts of Commodity FTRs [Abstract]
Notional Amount	16,190,000	[1]	5,989,000	[1]

[1] Amounts are not reflective of net positions in the underlying commodities.