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)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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- Definition

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

+ References

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)(3)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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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.

+ References

No definition available.

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 810
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=108788376&loc=d3e5747-111685

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Investments (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018
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%