SUPPLEMENTAL CASH FLOW INFORMATION - SUPPLEMENTAL INFORMATION (Details) - USD ($) $ in Millions	6 Months Ended
Jun. 30, 2025	Jun. 30, 2024
Supplemental cash flow information
Cash paid for interest, net of amount capitalized	$ 429.2	$ 377.7
Cash received for income taxes, net	(133.2)	(172.8)
Cash received from sale of production tax credits	113.0	173.0
Tax refund received from Wisconsin	25.0
Significant non-cash investing and financing transactions
Accounts payable related to construction costs	153.9	167.1
Common stock issued for stock-based compensation plans	3.2	6.4
Increase (decrease) in receivables related to property damage insurance proceeds	(1.4)	2.2
Liabilities accrued for software licensing agreements	$ 20.7	$ 0.0

Future cash outflow to pay for purchases of fixed assets that have occurred.

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Future cash outflow to pay for software licensing agreements already signed.

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