Pension and other PostRetirement Benefits - Expenses (Details) - CAD CAD in Millions	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016
Defined benefits pension plans
Pension and other PostRetirement Benefits,
Service cost	CAD 193	CAD 189
Interest cost	36	36
Defined benefit plans expense	229	225
Defined contribution plans expense	74	76
Total benefit plans expense charged to earnings	303	301
Return on plan assets (excluding amounts included in net interest expense)	(407)	(155)
Experience loss (gain) arising on plan liabilities	2	7
Actuarial loss arising from changes in financial assumptions	354	171
Actuarial (gain) loss arising from changes in demographic assumptions	(4)	8
Actuarial (gain) loss recognized in other comprehensive income	(55)	31
Defined benefits other post retirement benefits
Pension and other PostRetirement Benefits,
Service cost	14	13
Interest cost	22	23
Defined benefit plans expense	36	36
Total benefit plans expense charged to earnings	36	36
Experience loss (gain) arising on plan liabilities	(12)	(5)
Actuarial loss arising from changes in financial assumptions	26	(1)
Actuarial (gain) loss arising from changes in demographic assumptions	(9)	4
Actuarial (gain) loss recognized in other comprehensive income	CAD 5	CAD (2)

The decrease (increase) in a net defined benefit liability (asset) resulting from actuarial gains (losses) arising from experience adjustments that result in remeasurements of the net defined benefit liability (asset). Experience adjustments deal with the effects of differences between the previous actuarial assumptions and what has actually occurred. [Refer: Net defined benefit liability (asset)]

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 141
-Subparagraph c
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-URIDate 2017-03-09

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- Definition

Line items represent concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes of the table.

+ References

No definition available.

+ Details

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- Definition

The amount of other comprehensive income, before tax, related to gains (losses) on remeasurements of defined benefit plans, which comprise actuarial gains and losses; the return on plan assets, excluding amounts included in net interest on the net defined benefit liability (asset); and any change in the effect of the asset ceiling, excluding amounts included in net interest on the net defined benefit liability (asset). [Refer: Other comprehensive income, before tax; Defined benefit plans [member]; Plan assets [member]; Net defined benefit liability (asset)]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 1
-IssueDate 2017-01-01
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Reference 2: http://www.xbrl.org/2003/role/disclosureRef
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- Definition

The amount of post-employment benefit expense relating to defined benefit plans. [Refer: Defined benefit plans [member]]

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 5
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_5&doctype=Standard
-URIDate 2017-03-09

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- Definition

The amount of post-employment benefit expense relating to defined contribution plans. Defined contribution plans are post-employment benefit plans under which an entity pays fixed contributions into a separate entity (a fund) and will have no legal or constructive obligation to pay further contributions if the fund does not hold sufficient assets to pay all employee benefits relating to employee service in the current and prior periods.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 53
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_53&doctype=Standard
-URIDate 2017-03-09

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- Definition

The decrease (increase) in the net defined benefit liability (asset) resulting from the return on plan assets. The return on plans assets is interest, dividends and other revenue derived from the plan assets, together with realised and unrealised gains or losses on the plan assets, less any costs of managing plan assets and less any tax payable by the plan itself, other than tax included in the actuarial assumptions used to measure the present value of the defined benefit obligation. [Refer: Plan assets [member]; Net defined benefit liability (asset); Actuarial assumptions [member]]

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Name IAS
-Number 19
-IssueDate 2017-01-01
-Paragraph 141
-Subparagraph c
-Clause i
-URI http://eifrs.ifrs.org/eifrs/XBRL?type=IAS&num=19&date=2017-03-01&anchor=para_141_c_i&doctype=Standard
-URIDate 2017-03-09

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- Definition

The amount of actuarial loss (gain) arising from changes in demographic assumptions.

+ References

No definition available.

+ Details

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- Definition

The amount of actuarial loss (gain) arising from changes in financial assumptions.

+ References

No definition available.

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- Definition

Amount of interest expense recognized related to defined benefit plan.

+ References

No definition available.

+ Details

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- Definition

Amount of service cost expense recognized related to defined benefit plan.

+ References

No definition available.

+ Details

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- Definition

The combined amount of post-employment benefit expense relating to defined benefit and defined contribution plans.

+ References

No definition available.

+ Details

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