Debt (Capital Lease Obligations) (Details) - CAD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Leases, Capital [Abstract]
Interest imputed on capital leases	$ 1	$ 83
Capital lease obligations [Member]
Leases, Capital [Abstract]
Net carrying amount of properties which secures the capital lease obligations	$ 74	176
Capital lease obligations maturity start year	2019
Capital lease obligations maturity end year	2021
Capital lease obligations [Member] \| Minimum [Member]
Leases, Capital [Abstract]
Interest rate for capital lease obligations	1.80%
Capital lease obligations [Member] \| Maximum [Member]
Leases, Capital [Abstract]
Interest rate for capital lease obligations	4.30%
Equipment Leases [Member]
Leases, Capital [Abstract]
Capital lease assets acquired in period	$ 0	$ 30

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Debt Instrument, Maturity Year Range, Start

+ References

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=84164817&loc=d3e45280-112737

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- Definition

Amount of assets pledged to secure a debt instrument.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

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- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-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

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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

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