Fair Value of Financial Assets and Liabilities, Impact of Derivative Activity (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013
Financial Impact of Qualifying Fair Value Hedges on Earnings [Abstract]
Derivative instruments designated as fair value hedges	$ 0	$ 0	$ 0	$ 0
Recognized gains (losses) from fair value hedges or related hedged transactions	0	0	0	0
Cash Flow Hedging | Interest Rate Contract
Impact of Derivative Activity on Accumulated Other Comprehensive Loss Regulatory Assets and Liabilities and Income [Abstract]
Pre-tax losses reclassified into income during the period from accumulated other comprehensive loss	(100,000)	(100,000)	(100,000)	(100,000)
Other Derivative Instruments | Electric Commodity Contract
Impact of Derivative Activity on Accumulated Other Comprehensive Loss Regulatory Assets and Liabilities and Income [Abstract]
Pre-tax fair value losses recognized during the period in regulatory assets and liabilities	(1,000,000)		(2,400,000)
Pre-tax gains (losses) reclassified into income during the period from regulatory assets and liabilities	$ (1,900,000)		$ 900,000