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Commitments and Contingencies (Details) CAD in Millions, $ in Millions	3 Months Ended
	Dec. 31, 2017 CAD	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2014 USD ($)
Loss Contingency, Damages Sought, Value | CAD	CAD 10.0
Prior To 1995 [member]
Walter Energy tax assessment				$ 33.0
IRS-Walter Energy Claim 1 [Member]
Loss Contingency, Estimate of Possible Loss			$ 554.3
IRS-Walter Energy Claim 1 Priority [Member]
Loss Contingency, Estimate of Possible Loss		$ 229.1
IRS-Walter Energy Claim 2 [Member]
Loss Contingency, Estimate of Possible Loss		860.4
IRS-Walter Energy Claim 2 Priority [Member]
Loss Contingency, Estimate of Possible Loss		$ 535.3

X

- Definition

Total amount of tax claimed for issues at a former affiliate.

+ References

No definition available.

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- Definition

The value (monetary amount) of the award the plaintiff seeks in the legal matter.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14326-108349

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14557-108349

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-Section 50
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-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

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- Definition

Reflects the estimated amount of loss from the specified contingency as of the balance sheet date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 450
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=82911808&loc=d3e14435-108349

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-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 9
-Subparagraph (b)
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