DERIVATIVE INSTRUMENTS - DERIVATIVE ASSETS AND LIABILITIES (Details) $ in Millions	Mar. 31, 2022 USD ($) Instruments	Dec. 31, 2021 USD ($) Instruments
Derivative assets
Current derivative assets	$ 204.3	$ 107.0
Long-term derivative assets	14.8	13.0
Total derivative assets	219.1	120.0
Derivative liabilities
Current derivative liabilities	1.4	14.0
Long-term derivative liabilities	0.0	1.1
Total derivative liabilities	1.4	15.1
Natural gas contracts
Derivative assets
Current derivative assets	169.6	60.6
Long-term derivative assets	10.3	4.0
Derivative liabilities
Current derivative liabilities	1.4	14.0
Long-term derivative liabilities	0.0	1.1
FTRs
Derivative assets
Current derivative assets	1.0	2.4
Derivative liabilities
Current derivative liabilities	0.0	0.0
Coal contracts
Derivative assets
Current derivative assets	33.7	44.0
Long-term derivative assets	4.5	9.0
Derivative liabilities
Current derivative liabilities	0.0	0.0
Long-term derivative liabilities	$ 0.0	$ 0.0
Designated as hedging instrument
Derivative instruments
Number of derivative instruments \| Instruments	0	0

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

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