Pensions and other postretirement benefits (Details 3) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	CAD 17,761
Fair value of plan assets at end of year	17,917	CAD 17,761
Real Estate [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	317
Fair value of plan assets at end of year	357	317
Oil And Gas [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,374
Fair value of plan assets at end of year	1,012	1,374
Infrastructure [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	885
Fair value of plan assets at end of year	1,237	885
Fair Value Level 3 [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	2,156	1,978
Actual return relating to assets still held at the reporting date	(81)	25
Purchases	489	219
Sales	224	66
Fair value of plan assets at end of year	2,340	2,156
Fair Value Level 3 [Member] \| Equity [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	24	22
Actual return relating to assets still held at the reporting date	5	1
Purchases	3	4
Sales	8	3
Fair value of plan assets at end of year	24	24
Fair Value Level 3 [Member] \| Real Estate [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	317	299
Actual return relating to assets still held at the reporting date	(5)	21
Purchases	51	0
Sales	6	3
Fair value of plan assets at end of year	357	317
Fair Value Level 3 [Member] \| Oil And Gas [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	1,008	961
Actual return relating to assets still held at the reporting date	(242)	0
Purchases	0	47
Sales	0	0
Fair value of plan assets at end of year	766	1,008
Fair Value Level 3 [Member] \| Infrastructure [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	764	663
Actual return relating to assets still held at the reporting date	160	2
Purchases	405	159
Sales	204	60
Fair value of plan assets at end of year	1,125	764
Fair Value Level 3 [Member] \| Absolute Return [Member]
Defined Benefit Plan Fair Value Of Investments Disclosure [Line Items]
Fair value of plan assets at beginning of year	43	33
Actual return relating to assets still held at the reporting date	1	1
Purchases	30	9
Sales	6	0
Fair value of plan assets at end of year	CAD 68	CAD 43

Amount of increase in plan assets from purchases of investments.

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- Definition

Amount of decrease in plan assets from sales of investments.

+ References

No definition available.

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- Definition

Actual return on plan assets, separately identifying the amount related to assets still held at the reporting date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (d)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 5
-Subparagraph (c)(iv)(02)(A)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e2446-114920

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- Definition

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.

+ References

No definition available.

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 30
-Section 35
-Paragraph 50
-URI http://asc.fasb.org/extlink&oid=49178875&loc=d3e12355-114930

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 715
-SubTopic 20
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=58740216&loc=d3e1928-114920

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