Commitments and Contingencies (Other Commitments and Contingencies) (Narrative) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Self-Insurance [Member] \| Workers' Compensation, General and Automobile Policies [Member]
Loss Contingencies [Line Items]
Self-insurance reserve	$ 106.2	$ 85.8
Self-Insurance [Member] \| Workers' Compensation, General and Automobile Policies [Member] \| Other Long-Term Liabilities [Member]
Loss Contingencies [Line Items]
Self-insurance reserve, non-current	72.2	55.2
Self-Insurance [Member] \| Workers' Compensation, General and Automobile Policies [Member] \| Other Long-Term Assets [Member] \| Cash [Member]
Loss Contingencies [Line Items]
Cash collateral held by insurance carriers	1.6	1.5
Self-Insurance [Member] \| Employee Group Medical Claims Policy [Member]
Loss Contingencies [Line Items]
Self-insurance reserve	2.6	2.6
Performance and Payment Bonds [Member] \| Estimate [Member]
Loss Contingencies [Line Items]
Bonded projects, costs to complete	46.0	9.5
Performance and Payment Bonds [Member] \| Subsidiaries [Member]
Loss Contingencies [Line Items]
Outstanding bonds, amount	119.7	72.9
Surety Bonds [Member] \| Self-Insurance [Member] \| Workers' Compensation [Member]
Loss Contingencies [Line Items]
Outstanding bonds, amount	15.2	13.5
Credit Facility [Member]
Loss Contingencies [Line Items]
Letters of credit issued	157.1	314.3
Credit Facility [Member] \| Financial Guarantees [Member] \| Self-Insurance [Member] \| Workers' Compensation, General and Automobile Policies [Member]
Loss Contingencies [Line Items]
Letters of credit issued	$ 88.9	$ 85.1

Costs incurred and are directly related to generating contract revenues.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 225
-SubTopic 10
-Section S99
-Paragraph 2
-Subparagraph (SX 210.5-03.2(e))
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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)
-URI http://asc.fasb.org/extlink&oid=82913245&loc=d3e12069-110248

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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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+ 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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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
-Subparagraph (SX 210.5-02.24)
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