Derivative Instruments (Tables)

9 Months Ended

Sep. 30, 2014

Derivative Instruments (Tables) [Abstract]

Derivative instruments in balance sheet

	September 30, 2014				December 31, 2013
	Derivative Asset		Derivative Liability		Derivative Asset		Derivative Liability
	(Millions of Dollars)
Natural Gas	$	8.8	$	1.6	$	5.6	$	0.1
Fuel Oil	—		—		0.6		—
FTRs	10.1		—		3.5		—
Coal	5.5		—		2.1		0.2
Total	$	24.4	$	1.6	$	11.8	$	0.3

Derivative instruments' estimated notional volumes and gain (losses)

	Three Months Ended September 30, 2014				Three Months Ended September 30, 2013
	Volume	Gains (Losses)			Volume	Gains (Losses)
		(Millions of Dollars)				(Millions of Dollars)
Natural Gas	6.3 million Dth	$	(0.8	)	6.3 million Dth	$	(1.1	)
Fuel Oil	2.6 million gallons	—			2.5 million gallons	(0.1		)
FTRs	6.6 million MWh	2.0			6.9 million MWh	5.4
Total		$	1.2			$	4.2

	Nine Months Ended September 30, 2014			Nine Months Ended September 30, 2013
	Volume	Gains (Losses)		Volume	Gains (Losses)
		(Millions of Dollars)			(Millions of Dollars)
Natural Gas	31.1 million Dth	$	9.3	36.4 million Dth	$	(5.7	)
Fuel Oil	7.0 million gallons	0.6		6.2 million gallons	0.1
FTRs	19.7 million MWh	11.6		19.2 million MWh	11.0
Total		$	21.5		$	5.4

Offsetting Assets and Liabilities [Table Text Block]

	September 30, 2014						December 31, 2013
	Derivative			Derivative			Derivative		Derivative
	Asset			Liability			Asset		Liability
	(Millions of Dollars)
Gross Amount Recognized on the Balance Sheet	$	24.4		$	1.6		$	11.8	$	0.3
Gross Amount Not Offset on Balance Sheet (a)	(0.6		)	(1.6		)	—		—
Net Amount	$	23.8		$	—		$	11.8	$	0.3

(a) Gross Amount Not Offset on Balance Sheet includes cash collateral posted of $1.0 million and zero as of September 30, 2014 and December 31, 2013, respectively.