Derivatives (Narrative) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Derivative [Line Items]
Gain (Loss) on Components Excluded from Assessment of Price Risk Hedge Effectiveness			$ 8.2
Derivative Instruments, Gain (Loss) Recognized in Income, Ineffective Portion and Amount Excluded from Effectiveness Testing, Net			5.2
Current asset (liability) for the right to reclaim cash collateral	2.2	16.2
Net unrealized and realized gains (losses) related to trading portfolio	4.9	8.3
Gain on derivative contracts designated as hedge instruments in cash flow hedges to be reclassified from OCI into earnings during the next twelve months	0.8
Year One [Member]
Derivative [Line Items]
Value of trading portfolio realized	9.6
Diesel Purchases [Member] | Year One [Member]
Derivative [Line Items]
Percent of expected requirements covered	91.00%
Diesel Purchases [Member] | Year Two [Member]
Derivative [Line Items]
Percent of expected requirements covered	10.00%
Diesel Purchases [Member] | Heating Oil [Member]
Derivative [Line Items]
Quantities under derivative contracts	63,000,000
Diesel Purchases [Member] | Minimum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually	57,000,000
Diesel Purchases [Member] | Maximum [Member]
Derivative [Line Items]
Gallons of diesel fuel purchased annually	67,000,000
Diesel Usage Fuel Surcharges [Member] | Heating Oil [Member] | Year Two [Member]
Derivative [Line Items]
Quantities under derivative contracts	5,100,000
Heating Oil [Member] | Derivative [Member]
Derivative [Line Items]
Other Operating Income			$ 14.9