REGULATORY ASSETS AND LIABILITIES - REGULATORY ASSETS (Details) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Regulatory assets
Amounts recoverable from customers	$ 213.6	$ 20.0
Regulatory assets (June 30, 2021 includes $106.0 related to WEPCo Environmental Trust)	3,409.9	3,524.1
Total regulatory assets	3,623.5	3,544.1
Pension and OPEB costs
Regulatory assets
Total regulatory assets	1,054.4	1,101.6
Plant retirements
Regulatory assets
Total regulatory assets	729.1	740.8
Environmental remediation costs
Regulatory assets
Total regulatory assets	609.3	638.2
Income tax related items
Regulatory assets
Total regulatory assets	459.1	454.6
Energy costs recoverable through rate adjustments
Regulatory assets
Total regulatory assets	203.3	1.1
Asset retirement obligations
Regulatory assets
Total regulatory assets	190.7	181.3
SSR
Regulatory assets
Total regulatory assets	132.8	135.6
Securitization
Regulatory assets
Total regulatory assets	106.0	105.2
Uncollectible expense
Regulatory assets
Total regulatory assets	41.2	82.0
Derivatives
Regulatory assets
Total regulatory assets	7.1	26.5
Other, net
Regulatory assets
Total regulatory assets	$ 90.5	$ 77.2

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The amount for the individual regulatory asset as itemized in a table of regulatory assets as of the end of the period.

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Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 340
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=6499975&loc=d3e44250-110382

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