Length of transmission line.

No definition available.

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- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

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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

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- Definition

The cash outflow associated with the purchase of or advances to an 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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 13
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3213-108585

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- Definition

Cash dividends or other distributions received from unconsolidated subsidiaries, certain corporate joint ventures, and certain noncontrolled corporations that are returns of capital. Excludes dividends or distributions from equity method investments classified as operating activities.

+ References

No definition available.

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Commitments and Contingencies (Investments in Affiliates and Other Entities) - Additional Information (Detail) $ in Millions	24 Months Ended
	Sep. 30, 2016 USD ($) km	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Other Commitments, Planned Oil and Gas Infrastructure Projects [Member]
Other Commitments [Line Items]
Outstanding capital commitment	$ 4.2
Scenario Forecast [Member] \| Other Commitments, Planned Oil and Gas Infrastructure Projects [Member]
Other Commitments [Line Items]
Outstanding capital commitment		$ 3.7	$ 0.5
Alberta Power Line [Member]
Other Commitments [Line Items]
Length of electrical transmission line to be constructed under contract \| km	500
Aggregate contributions to this unconsolidated affiliate	$ 9.8
Proceeds from return of capital	$ 2.3