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Employee Benefit Plans (Assumptions Used in Accounting for Defined Benefit Pension and Other Post-retirement Benefit Plans) (Details) - CAD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
An increase or decrease of one percentage point of the assumed health care cost trend
Service cost and interest cost, Increase	$ 1
Service cost and interest cost, Decrease	(1)
Accumulated post-retirement benefit obligation, December 31, Increase	16
Accumulated post-retirement benefit obligation, December 31, Decrease	(14)
A 25 basis point change in the discount rate and asset return assumptions
Discount rate assumption, Increase	(9)
Discount rate assumption, Decrease	9
Asset rate assumption, Increase	(6)
Asset rate assumption, Decrease	$ 6
Defined benefit pension plans
Benefit obligation - December 31:
Discount rate - past service	3.17%	4.05%
Discount rate - future service	3.21%	4.05%
Rate of compensation increase	3.32%	3.30%
Health care trend - initial (next year)	0.00%	0.00%
Health care trend - ultimate	0.00%	0.00%
Benefit cost for year ended December 31:
Discount rate - past and future service	4.05%	3.55%
Expected long-term return on plan assets	6.50%	6.38%
Rate of compensation increase	3.30%	3.12%
Health care trend - initial (next year)	0.00%	0.00%
Health care trend - ultimate	0.00%	0.00%
Non-pension Benefit Plans
Benefit obligation - December 31:
Discount rate - past service	3.27%	4.30%
Discount rate - future service	3.28%	4.30%
Rate of compensation increase	3.70%	3.67%
Health care trend - initial (next year)	6.15%	6.39%
Health care trend - ultimate	4.38%	4.45%
Health care trend - year ultimate reached	2038	2035
Benefit cost for year ended December 31:
Discount rate - past and future service	4.30%	3.65%
Expected long-term return on plan assets	2.81%	3.73%
Rate of compensation increase	3.67%	3.28%
Health care trend - initial (next year)	6.39%	6.65%
Health care trend - ultimate	4.45%	4.45%
Health care trend - year ultimate reached	2035	2036

X

- Definition

The decrease in plan assets based on a 25 basis points (0.25 percent) change.

+ References

No definition available.

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- Definition

The increase in plan assets based on a 25 basis points (0.25 percent) change.

+ References

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- Definition

The decrease from a 25 basis points (0.25 percent) change on the discount rate.

+ References

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- Definition

The increase from a 25 basis points (0.25 percent) change on the discount rate.

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- Definition

The assumed health care cost trend rate related to net periodic benefits costs for the next year used to measure the expected cost of benefits covered by the plan (gross eligible charges). This is based upon the annual rate of change in the cost of health care benefits currently provided by the postretirement benefit plan, due to factors other than changes in the composition of the plan population by age and dependency status.

+ References

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The ultimate trend rate for health care costs related to net periodic benefits costs.

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- Definition

Year the ultimate health care cost trend rate related to net periodic benefits costs is expected to be reached, in CCYY format.

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- Definition

Interest rate used to discount liability to provide future service related to continuing-care contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 954
-SubTopic 440
-Section 50
-Paragraph 1
-Subparagraph (c)
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Weighted average rate for present value of future retirement benefits cash flows, used to determine benefit obligation of defined benefit plan.

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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- Definition

Weighted average rate increase of compensation, used to determine benefit obligation of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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- Definition

Weighted average rate for present value of future retirement benefits cash flows, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Weighted average rate of return on plan assets, reflecting average rate of earnings expected on existing plan assets and expected contributions, used to determine net periodic benefit cost of defined benefit plan.

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- Definition

Weighted average rate of compensation increase used to determine net periodic benefit cost of defined benefit plan. Plan includes, but is not limited to, pay-related defined benefit plan.

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- Definition

Amount of decrease in accumulated postretirement benefit obligation from one-percentage-point decrease in assumed health care cost trend rate.

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Amount of decrease in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point decrease in assumed health care cost trend rate.

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Amount of increase in accumulated postretirement benefit obligation from one-percentage-point increase in assumed health care cost trend rate.

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Amount of increase in service and interest cost components of net periodic postretirement benefit cost from one-percentage-point increase in assumed health care cost trend rate.

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Assumed rate, for next fiscal year, based on annual change in cost of health care cost benefits used to measure expected cost of benefits covered by defined benefit postretirement plan. Factors include, but are not limited to, estimate of health care inflation, change in health care utilization or delivery pattern, technological advances, and change in health status of participant. Excludes factors for change in composition of plan population by age and dependency status.

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Ultimate trend rate for health care cost for defined benefit postretirement plan.

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Year ultimate health care cost trend rate is expected to be reached, in CCYY format.

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