VARIABLE INTEREST ENTITIES (Details) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($) MW
ATC
Variable interest entities
Ownership interest (as a percent)	60.00%
ATC Holdco
Variable interest entities
Ownership interest (as a percent)	75.00%
Power purchase agreement
Variable interest entities
Firm capacity from power purchase agreement (in megawatts) \| MW	236
Minimum energy requirements over remaining term of power purchase agreement (in megawatts) \| MW	0
Remaining term of power purchase agreement (in years)	1 year
Residual guarantee associated with power purchase agreement \| $	$ 0.0
Required payments over remaining term of power purchase agreement \| $	$ 11.2

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
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Under long-term contracts with public utility districts, cooperatives or other organizations, a utility company receives a portion of the output of a production plant constructed and financed by the district or cooperative. The utility has only a nominal or no investment at all in the plant but pays a proportionate part of the plant's costs, including debt service.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 980
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 10.D)
-URI http://asc.fasb.org/extlink&oid=6499423&loc=d3e659339-123030

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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- Definition

Firm capacity, in megawatts, from a power purchase agreement accounted for as a finance lease.

+ References

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- Definition

The minimum energy requirements, in megawatts, over the remaining term of a power purchase agreement accounted for as a finance lease.

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- Definition

The remaining term, in years, of a power purchase agreement accounted for as a finance lease.

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- Definition

Amount of the residual guarantee associated with a power purchase agreement accounted for as a finance lease.

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