Derivative Instruments (Tables)

12 Months Ended

Dec. 31, 2016

Derivative Instruments and Hedging Activities Disclosure [Abstract]

Derivative assets and liabilities

The following table shows our derivative assets and derivative liabilities:

	December 31, 2016				December 31, 2015
(in millions)	Derivative Assets		Derivative Liabilities		Derivative Assets		Derivative Liabilities
Other current
Natural gas contracts	$	31.4	$	0.4	$	2.6	$	38.5
Petroleum products contracts	0.2		0.1		0.9		3.8
FTRs	5.1		—		3.6		—
Coal contracts	1.5		1.4		1.7		6.7
Total other current	$	38.2	$	1.9	$	8.8	$	49.0
Other long-term
Natural gas contracts	$	2.9	$	—	$	0.5	$	3.3
Petroleum products contracts	—		—		0.3		1.1
Coal contracts	0.5		0.5		0.3		5.6
Total other long-term	$	3.4	$	0.5	$	1.1	$	10.0
Total	$	41.6	$	2.4	$	9.9	$	59.0

Estimated notional volumes and realized gain (losses)

Our estimated notional sales volumes and realized gains (losses) were as follows:

	December 31, 2016				December 31, 2015				December 31, 2014
(in millions)	Volume	Gains (Losses)			Volume	Gains (Losses)			Volume	Gains
Natural gas contracts	151.1 Dth	$	(59.6	)	86.2 Dth	$	(50.5	)	40.5 Dth	$	7.3
Petroleum products contracts	14.7 gallons	(3.2		)	7.8 gallons	(1.9		)	9.2 gallons	0.5
FTRs	33.7 MWh	13.3			27.3 MWh	6.7			26.1 MWh	12.7
Total		$	(49.5	)		$	(45.7	)		$	20.5

Offsetting Assets and Liabilities

The following table shows derivative assets and derivative liabilities if derivative instruments by counterparty were presented net on our balance sheets:

	December 31, 2016						December 31, 2015
(in millions)	Derivative Assets			Derivative Liabilities			Derivative Assets			Derivative Liabilities
Gross amount recognized on the balance sheet	$	41.6		$	2.4		$	9.9		$	59.0
Gross amount not offset on the balance sheet *	(4.9		)	(0.5		)	(3.0		)	(22.5		)
Net amount	$	36.7		$	1.9		$	6.9		$	36.5

* Includes cash collateral received of $4.4 million at December 31, 2016, and cash collateral posted of $19.5 million at December 31, 2015.