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EMPLOYEE BENEFITS - Summary of Changes in Plan Assets and Benefit Obligations (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2021 | Dec. 31, 2020
Pension Plan |  |
Net Regulatory Assets [Abstract] |  |
Actuarial (Gains)/Losses Arising During the Year | $ (961.7) | $ 553.1
Actuarial Losses Reclassified as Net Periodic Benefit Expense | (231.2) | (194.3)
Prior Service Cost Arising During the Year | 0.0 | 2.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | (1.3) | (1.0)
Actuarial Loss | 1,427.3 | 2,620.2
Prior Service Cost | 5.3 | 6.6
OCI |  |
Actuarial (Gains)/Losses Arising During the Year | (28.4) | 24.3
Actuarial Losses Reclassified as Net Periodic Benefit Expense | (12.7) | (7.7)
Prior Service Cost Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | (0.1) | (0.2)
Actuarial Loss | 66.3 | 107.4
Prior Service Cost | 0.6 | 0.7
Other Postretirement Benefits Plan |  |
Net Regulatory Assets [Abstract] |  |
Actuarial (Gains)/Losses Arising During the Year | (181.5) | 39.1
Actuarial Losses Reclassified as Net Periodic Benefit Expense | (8.5) | (8.0)
Prior Service Cost Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | 21.1 | 21.3
Actuarial Loss | 45.0 | 235.0
Prior Service Cost | (130.1) | (151.2)
OCI |  |
Actuarial (Gains)/Losses Arising During the Year | (4.0) | 1.3
Actuarial Losses Reclassified as Net Periodic Benefit Expense | (0.4) | (0.4)
Prior Service Cost Arising During the Year | 0.0 | 0.0
Prior Service (Cost)/Credit Reclassified as Net Periodic Benefit (Expense)/Income | 0.1 | (0.1)
Actuarial Loss | 3.5 | 7.9
Prior Service Cost | $ 1.0 | $ 0.9

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- Definition The change in other regulatory asset due to the amortization of the net prior service costs (credit) into net periodic pension costs. + References No definition available. + Details
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- Definition Pretax change in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan, that has not been recognized in net periodic benefit cost. + References No definition available. + Details
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- Definition he net gain (loss) previously recognized in regulatory assets that is a reclassification adjustment of other comprehensive income as a result of being recognized as a component of net periodic benefit cost for the period. + References No definition available. + Details
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- Definition Amount related to the pretax cost of benefit changes attributable to plan participants' prior service pursuant to a plan amendment or a plan initiation, which has not yet been recognized as components of net periodic benefit cost. + References No definition available. + Details
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- Definition The pretax net amount of gains and losses that are not yet recognized as a component of net periodic benefit cost, and that are recognized as increases or decreases in other comprehensive income as they arise. Gains and losses are due to changes in the value of either the benefit obligation or the plan assets resulting from experience different from that assumed or from a change in an actuarial assumption, or the consequence of a decision to temporarily deviate from the substantive plan. + References No definition available. + Details
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- Definition Amount, before tax, of accumulated other comprehensive income (loss) for gain (loss) of defined benefit plan, that has not been recognized in net periodic benefit (cost) credit. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (j) -URI http://asc.fasb.org/extlink&oid=123447040&loc=d3e1928-114920 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=124509347&loc=SL7669686-108580 + Details
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