REGULATORY ASSETS AND LIABILITIES - REGULATORY ASSETS (Details) $ in Millions	12 Months Ended
Dec. 31, 2021 USD ($) utility	Dec. 31, 2020 USD ($)
Regulatory assets
Regulatory assets	$ 347.9	$ 449.4
Allowance for return on equity capitalized for regulatory purposes	12.3	16.6
Regulatory assets not earning a return	32.4
Estimated future cash expenditures for environmental remediation	95.0	88.3
Environmental remediation costs
Regulatory assets
Regulatory assets	120.1	116.1
Cash expenditures for environmental remediation costs	25.1
Estimated future cash expenditures for environmental remediation	95.0
Pension and OPEB costs
Regulatory assets
Regulatory assets	74.1	161.4
Income tax related items
Regulatory assets
Regulatory assets	54.5	46.7
Plant retirement related items
Regulatory assets
Regulatory assets	50.2	58.5
ReACT
Regulatory assets
Regulatory assets	15.6	18.2
Asset retirement obligations (AROs)
Regulatory assets
Regulatory assets	14.2	13.1
Uncollectible expense
Regulatory assets
Regulatory assets	5.5	12.5
Forward Wind Energy Center
Regulatory assets
Regulatory assets	$ 2.8	10.3
Recovery period of regulatory asset	2 years
Number of utilities along with WPS that entered in an agreement to purchase generation facility \| utility	2
Other, net
Regulatory assets
Regulatory assets	$ 10.9	$ 12.6

Amount of cash outflow to settle environmental loss contingencies.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
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-Name Accounting Standards Codification
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