Number of joint ventures in which the Company has an interest.

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The percentage interest in a proportionately consolidated joint venture.

+ References

No definition available.

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- Definition

Costs incurred and are directly related to generating contract revenues.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
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- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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No definition available.

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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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No definition available.

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Amount of cash outflow reducing loss contingency liability.

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Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
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Amount charged against operating income increasing loss contingency liability, after adjustments to reduce previously estimated charges.

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Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers.

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No definition available.

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The fair value, as of the date of each statement of financial position presented, of other assets which are owned but transferred to serve as collateral for the payment of the related debt obligation, and that are reclassified and separately reported in the statement of financial position because the transferee has the right by contract or custom to sell or re-pledge them.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=66007379&loc=d3e113888-111728

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- Definition

Carrying amount (including both current and noncurrent portions) of accrued known and estimated losses incurred as of the balance sheet date for which no insurance coverage exists, and for which a claim has been made or is probable of being asserted, typically arising from workmen's compensation-type of incidents and personal injury to nonemployees from accidents on the entity's property.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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Carrying amount of accrued known and estimated losses incurred as of the balance sheet date for which no insurance coverage exists, and for which a claim has been made or is probable of being asserted, typically arising from workmen's compensation-type of incidents and personal injury to nonemployees from accidents on the entity's property that are expected to be paid after one year (or the normal operating cycle, if longer).

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No definition available.

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Commitments and Contingencies (Other Commitments and Contingencies) (Narrative) (Details) CAD in Millions, $ in Millions			3 Months Ended	61 Months Ended
	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2017 CAD	Sep. 30, 2017 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2016 USD ($)	Nov. 30, 2011 USD ($)
Central States Southeast and Southwest Areas Pension Fund [Member] \| Multiemployer Plans, Pension [Member]
Commitments and Contingencies [Line Items]
Multiemployer plans, withdrawal obligation, amount									$ 6.4
Multiemployer plans, withdrawal obligation, payments				$ 6.4
Multiemployer plans, withdrawal obligation, expected settlement, expense			$ 0.6
Self-Insurance [Member] \| Workers Compensation, General and Automobile Policies [Member]
Commitments and Contingencies [Line Items]
Self-insurance reserve						$ 98.5		$ 85.8
Self-Insurance [Member] \| Workers Compensation, General and Automobile Policies [Member] \| Other Long-Term Liabilities [Member]
Commitments and Contingencies [Line Items]
Self-insurance reserve, non-current						67.5		55.2
Self-Insurance [Member] \| Workers Compensation, General and Automobile Policies [Member] \| Other Long-Term Assets [Member] \| Cash [Member]
Commitments and Contingencies [Line Items]
Cash collateral deposited with insurance carriers						1.5		1.5
Self-Insurance [Member] \| Employee Group Medical Claims Policies [Member]
Commitments and Contingencies [Line Items]
Self-insurance reserve						$ 2.6		2.6
Joint Ventures [Member] \| Joint Ventures That Provide Infrastructure Construction Services For Electrical Transmission Projects [Member]
Commitments and Contingencies [Line Items]
Number of joint ventures					7	7
Joint Ventures [Member] \| Joint Ventures That Provide Infrastructure Construction Services For Electrical Transmission Projects [Member] \| Minimum [Member]
Commitments and Contingencies [Line Items]
Proportionately consolidated non-controlled joint venture, percentage interest					85.00%	85.00%
Joint Ventures [Member] \| Joint Ventures That Provide Infrastructure Construction Services For Electrical Transmission Projects [Member] \| Maximum [Member]
Commitments and Contingencies [Line Items]
Proportionately consolidated non-controlled joint venture, percentage interest					90.00%	90.00%
Joint Ventures [Member] \| Pacer [Member]
Commitments and Contingencies [Line Items]
Proportionately consolidated non-controlled joint venture, percentage interest					35.00%	35.00%
Performance and Payment Bonds [Member]
Commitments and Contingencies [Line Items]
Outstanding bonds, amount						$ 119.2		72.9
Performance and Payment Bonds [Member] \| Joint Ventures [Member] \| Pacer [Member]
Commitments and Contingencies [Line Items]
Outstanding bonds, amount \| CAD					CAD 132.1		CAD 132.1
Performance and Payment Bonds [Member] \| Estimate [Member]
Commitments and Contingencies [Line Items]
Bonded projects, costs to complete	$ 51.3	$ 9.5
Surety Bond [Member] \| Self-Insurance [Member] \| Workers Compensation [Member]
Commitments and Contingencies [Line Items]
Outstanding bonds, amount						13.7		13.5
Credit Facility [Member]
Commitments and Contingencies [Line Items]
Letters of credit issued						189.1		314.3
Credit Facility [Member] \| Financial Guarantees [Member] \| Self-Insurance [Member] \| Workers Compensation, General and Automobile Policies [Member]
Commitments and Contingencies [Line Items]
Letters of credit issued						$ 84.6		$ 85.1