Long-term Debt (Capital Lease Obligations) (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Capital lease obligations [Abstract]
Interest imputed on capital leases	CAD 83	CAD 95
Capital Lease Obligations [Member]
Capital lease obligations [Abstract]
Net carrying amount of properties which secures the capital lease obligations	CAD 176	403
Capital lease obligations maturity start year	2018
Capital lease obligations maturity end year	2037
Capital Lease Obligations [Member] \| Minimum [Member]
Capital lease obligations [Abstract]
Interest rate for capital lease obligations	1.00%
Capital Lease Obligations [Member] \| Maximum [Member]
Capital lease obligations [Abstract]
Interest rate for capital lease obligations	6.80%
Equipment Leases [Member]
Capital lease obligations [Abstract]
Capital lease assets acquired in period	CAD 30	CAD 57

Latest year the outstanding debt instruments are required to be repaid in CCYY format.

No definition available.

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- Definition

Earliest year the outstanding debt instruments are required to be repaid in CCYY format.

+ References

No definition available.

+ Details

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- Definition

Amount necessary to reduce net minimum lease payments to present value for capital leases.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6455398&loc=d3e45280-112737

+ Details

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Period Type:	instant

- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=6479336&loc=d3e64711-112823

+ Details

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Balance Type:	debit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ 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 210.5-02.22(a)(1))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

+ Details

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- References

No definition available.

+ Details

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- Definition

Amount of acquisition of long-lived, physical assets used in the normal conduct of business and not intended for resale. Examples include, but are not limited to, land, buildings, machinery and equipment, office equipment, furniture and fixtures, and computer equipment.

+ References

No definition available.

+ Details

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