Weighted average amortization period of finite-lived intangible assets acquired either individually or as part of a group of assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The aggregate amount of recurring noncash expense charged against earnings in the period to allocate the cost of assets over their estimated remaining economic lives.

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Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Accumulated amount of amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in next fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fifth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in fourth fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in third fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount of amortization for assets, excluding financial assets and goodwill, lacking physical substance with finite life expected to be recognized in second fiscal year following current fiscal year. Excludes interim and annual periods when interim periods are reported from current statement of financial position date (rolling approach).

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Amount before amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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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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Amount after amortization of assets, excluding financial assets and goodwill, lacking physical substance with a finite life.

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Period of amortization over a future period of time

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GOODWILL AND INTANGIBLES - INTANGIBLE LIABILITIES (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Mar. 31, 2022	Dec. 31, 2022
Finite-Lived Intangible Liabilities
Amortization	$ 10.4	$ 2.2
Period of amortization	5 years
Amortization to be recorded as an increase to operating revenues
Amortization to be recorded in the next five years
2023	$ 50.4
2024	53.4
2025	53.4
2026	53.4
2027	53.4
Amortization to be recorded as a decrease to other operation and maintenance
Amortization to be recorded in the next five years
2023	0.2
2024	0.2
2025	0.2
2026	0.2
2027	0.2
WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	665.8		$ 355.8
Accumulated amortization	(30.8)		(20.4)
Net carrying amount	635.0		335.4
PPAs \| WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	653.9		343.9
Accumulated amortization	(27.1)		(16.9)
Net carrying amount	$ 626.8		327.0
PPAs \| Blooming Grove , Tatanka Ridge, Jayhawk, Thunderhead, Samson I, and Sapphire Sky
Finite-Lived Intangible Liabilities
Weighted average life	12 years
Proxy revenue swap \| WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	$ 7.2		7.2
Accumulated amortization	(2.9)		(2.8)
Net carrying amount	$ 4.3		4.4
Proxy revenue swap \| Upstream
Finite-Lived Intangible Liabilities
Weighted average life	6 years
Length of proxy revenue contract, in years	10 years
Interconnection agreements \| WECI
Finite-Lived Intangible Liabilities
Gross carrying amount	$ 4.7		4.7
Accumulated amortization	(0.8)		(0.7)
Net carrying amount	$ 3.9		$ 4.0
Interconnection agreements \| Tatanka Ridge and Bishop Hill III
Finite-Lived Intangible Liabilities
Weighted average life	18 years