FAIR VALUE MEASUREMENTS (Tables)

3 Months Ended

Mar. 31, 2021

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:

	March 31, 2021
(in millions)	Level 1		Level 2		Level 3		Total
Derivative assets
Natural gas contracts	$	12.3	$	1.6	$	—	$	13.9
FTRs	—		—		0.9		0.9
Coal contracts	—		2.6		—		2.6
Total derivative assets	$	12.3	$	4.2	$	0.9	$	17.4
Investments held in rabbi trust	$	71.6	$	—	$	—	$	71.6
Derivative liabilities
Natural gas contracts	$	3.1	$	1.0	$	—	$	4.1
Coal contracts	—		0.3		—		0.3
Interest rate swaps	—		5.1		—		5.1
Total derivative liabilities	$	3.1	$	6.4	$	—	$	9.5

	December 31, 2020
(in millions)	Level 1		Level 2		Level 3		Total
Derivative assets
Natural gas contracts	$	11.7	$	2.0	$	—	$	13.7
FTRs	—		—		2.4		2.4
Coal contracts	—		1.8		—		1.8
Total derivative assets	$	11.7	$	3.8	$	2.4	$	17.9
Investments held in rabbi trust	$	79.6	$	—	$	—	$	79.6
Derivative liabilities
Natural gas contracts	$	7.7	$	6.4	$	—	$	14.1
Coal contracts	—		1.2		—		1.2
Interest rate swaps	—		6.8		—		6.8
Total derivative liabilities	$	7.7	$	14.4	$	—	$	22.1

Reconciliation 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:

	Three Months Ended March 31
(in millions)	2021		2020
Balance at the beginning of the period	$	2.4	$	3.1
Purchases	0.1		—
Settlements	(1.6)		(2.2)
Balance at the end of the period	$	0.9	$	0.9

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 were not recorded at fair value:

	March 31, 2021				December 31, 2020
(in millions)	Carrying Amount		Fair Value		Carrying Amount		Fair Value
Preferred stock of subsidiary	$	30.4	$	29.9	$	30.4	$	32.3
Long-term debt, including current portion (1)	13,041.8		14,139.0		12,450.5		14,343.2

(1)The carrying amount of long-term debt excludes finance lease obligations of $62.9 million and $63.4 million at March 31, 2021 and December 31, 2020, respectively.