Derivative Instruments (Tables)

3 Months Ended

Mar. 31, 2014

Derivative Instruments (Tables) [Abstract]

Derivative instruments in balance sheet

	March 31, 2014				December 31, 2013
	Derivative Asset		Derivative Liability		Derivative Asset		Derivative Liability
	(Millions of Dollars)
Natural Gas	$	6.1	$	—	$	5.6	$	0.1
Fuel Oil	0.1		—		0.6		—
FTRs	1.7		—		3.5		—
Coal	1.3		0.1		2.1		0.2
Total	$	9.2	$	0.1	$	11.8	$	0.3

Derivative instruments' estimated notional volumes and gain (losses)

	Three Months Ended March 31, 2014			Three Months Ended March 31, 2013
	Volume	Gains (Losses)		Volume	Gains (Losses)
		(Millions of Dollars)			(Millions of Dollars)
Natural Gas	14.9 million Dth	$	7.6	18.8 million Dth	$	(6.5	)
Fuel Oil	2.0 million gallons	0.2		1.6 million gallons	0.1
FTRs	5.7 million MWh	7.0		5.8 million MWh	0.9
Total		$	14.8		$	(5.5	)

Offsetting Assets and Liabilities [Table Text Block]

	March 31, 2014				December 31, 2013
	Derivative		Derivative		Derivative		Derivative
	Asset		Liability		Asset		Liability
	(Millions of Dollars)
Gross Amount Recognized on the Balance Sheet	$	9.2	$	0.1	$	11.8	$	0.3
Gross Amount Not Offset on Balance Sheet (a)	—		—		—		—
Net Amount	$	9.2	$	0.1	$	11.8	$	0.3

(a) Gross Amount Not Offset on Balance Sheet includes no cash collateral posted as of March 31, 2014 and December 31, 2013.