REGULATORY ASSETS AND LIABILITIES - REGULATORY ASSETS (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Regulatory assets
Amounts recoverable from customers	$ 134.2	$ 102.3
Regulatory assets	3,144.7	3,264.8
Total regulatory assets	3,278.9	3,367.1
Pension and OPEB costs
Regulatory assets
Total regulatory assets	762.6	802.3
Plant retirement related items
Regulatory assets
Total regulatory assets	705.9	722.3
Environmental remediation costs
Regulatory assets
Total regulatory assets	621.6	630.9
Income tax related items
Regulatory assets
Total regulatory assets	457.0	458.8
Asset retirement obligations
Regulatory assets
Total regulatory assets	180.6	194.2
System support resource
Regulatory assets
Total regulatory assets	126.7	129.5
Energy costs recoverable through rate adjustments
Regulatory assets
Total regulatory assets	120.0	85.4
Securitization
Regulatory assets
Total regulatory assets	96.1	100.7
MERC extraordinary natural gas costs
Regulatory assets
Total regulatory assets	47.1	59.7
Derivatives
Regulatory assets
Total regulatory assets	38.5	33.1
Uncollectible expense
Regulatory assets
Total regulatory assets	30.0	42.6
Energy efficiency programs
Regulatory assets
Total regulatory assets	23.9	22.0
Other, net
Regulatory assets
Total regulatory assets	$ 68.9	$ 85.6

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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.

+ References

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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Carrying amount as of the balance sheet date of capitalized costs of regulated entities that are expected to be recovered through revenue sources within one year or the normal operating cycle, if longer. Such costs are capitalized if they meet both of the following criteria: a. It is probable that future revenue in an amount at least equal to the capitalized cost will result from inclusion of that cost in allowable costs for rate-making purposes. b. Based on available evidence, the future revenue will be provided to permit recovery of the previously incurred cost rather than to provide for expected levels of similar future costs. If the revenue will be provided through an automatic rate-adjustment clause, this criterion requires that the regulator's intent clearly be to permit recovery of the previously incurred cost.

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