Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2019

Fair Value Disclosures [Abstract]

Schedule of fair value of assets and liabilities measured on a recurring basis categorized by level within the fair value hierarchy

The following tables summarize our financial assets and liabilities that were accounted for at fair value on a recurring basis, categorized by level within the fair value hierarchy:

	December 31, 2019
(in millions)	Level 1		Level 2		Level 3		Total
Derivative assets
Natural gas contracts	$	0.4	$	—	$	—	$	0.4
FTRs	—		—		1.5		1.5
Coal contracts	—		0.1		—		0.1
Total derivative assets	$	0.4	$	0.1	$	1.5	$	2.0
Derivative liabilities
Natural gas contracts	$	5.2	$	—	$	—	$	5.2
Coal contracts	—		0.2		—		0.2
Total derivative liabilities	$	5.2	$	0.2	$	—	$	5.4

	December 31, 2018
(in millions)	Level 1		Level 2		Level 3		Total
Derivative assets
Natural gas contracts	$	0.7	$	—	$	—	$	0.7
FTRs	—		—		4.4		4.4
Total derivative assets	$	0.7	$	—	$	4.4	$	5.1
Derivative liabilities
Natural gas contracts	$	1.2	$	—	$	—	$	1.2
Coal contracts	—		0.1		—		0.1
Total derivative liabilities	$	1.2	$	0.1	$	—	$	1.3

Reconcilation of changes in fair value of items categorized as level 3 measurements

The following table summarizes the changes to derivatives classified as Level 3 in the fair value hierarchy at December 31:

(in millions)	2019			2018			2017
Balance at the beginning of the period	$	4.4		$	2.4		$	3.1
Purchases	6.8			9.4			6.9
Settlements	(9.7		)	(7.4		)	(7.6		)
Balance at the end of the period	$	1.5		$	4.4		$	2.4

Schedule of carrying value and estimated fair value of financial instruments not recorded at fair value

The following table shows the financial instruments included on our balance sheets that are not recorded at fair value:

	December 31, 2019				December 31, 2018
(in millions)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Preferred stock	$	30.4	$	29.5	$	30.4	$	28.3
Long-term debt, including current portion	2,759.2		3,209.5		2,709.6		2,881.6