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

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Amount of gain (loss) on sale or disposal of an equity method investment.

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This item represents the entity's ownership percentage in the investee multiplied by the investee's total equity.

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The cash inflow associated with the sale of equity method investments, which are investments in joint ventures and entities in which the entity has an equity ownership interest normally of 20 to 50 percent and exercises significant influence.

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The reporting entity's maximum amount of exposure to loss as a result of its involvement with the Variable Interest Entity (VIE).

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Investments (Details) - USD ($) $ in Millions	3 Months Ended
Investments (Details) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Jun. 30, 2019
Schedule of Equity Method Investments [Line Items]
Investment balance in TWH		$ 13.4	$ 13.4	$ 13.4
Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount		$ 13.4	$ 13.4	$ 13.4
Northwest Holdings [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage of TWH		50.00%
TransCanada American Investments Ltd. [Member]
Schedule of Equity Method Investments [Line Items]
Ownership percentage of TWH		50.00%
Subsequent Event [Member]
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Realized Gain (Loss) on Disposal	$ 0.5
Forecast [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Equity Method Investments	14.0
Cash and Cash Equivalents [Member] \| Subsequent Event [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Equity Method Investments	7.0
Cash and Cash Equivalents [Member] \| Forecast [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Equity Method Investments	7.0
Notes Receivable [Member] \| Subsequent Event [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Equity Method Investments	7.0
Notes Receivable [Member] \| Forecast [Member]
Schedule of Equity Method Investments [Line Items]
Proceeds from Sale of Equity Method Investments	$ 7.0