Stock-based Compensation (Employee Share Investment Plan) (Details) - Employee Share Investment Plan [Member] shares in Millions	12 Months Ended
Dec. 31, 2019 CAD ($) participants shares	Dec. 31, 2018 participants shares	Dec. 31, 2017 participants shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum percentage of gross salary eligible employees can subscribe to purchase shares of Company's common stock on the open market	10.00%
Maximum percentage of additional contribution made by the Company of amount invested by employee	35.00%
Maximum percentage of gross salary employer can contribute toward purchase of Company's common stock	6.00%
Vesting period	1 year
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Unvested contributions, December 31, 2018 (in shares)	0.0
Company contributions (in shares)	0.3
Unvested contributions, December 31, 2019 (in shares)	0.3	0.0
Weighted average fair value of shares contributed \| $	$ 118.83
Number of participants holding shares \| participants	21,674	22,185	19,642
Number of shares purchased on behalf of employees (in shares)	1.5	1.8	1.7

Employee Stock Ownership Plan (ESOP), Shares Contributed To ESOP, Weighted Average Fair Value

No definition available.

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- Definition

The number of employees participating in the plan and holding shares at the balance sheet date.

+ References

No definition available.

+ Details

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- Definition

The Company will invest, on the employee's behalf, this percentage of the amount invested by the employees, up to 6 % of the employee's gross salary.

+ References

No definition available.

+ Details

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- Definition

The highest percentage of annual salary that the employer will contribute toward purchase with respect to the plan.

+ References

No definition available.

+ Details

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- Definition

The shares or units in an ESOP trust that have been assigned to individual participant accounts based on a known formula. IRS rules require allocations to be nondiscriminatory generally based on compensation, length of service, or a combination of both. For any particular participant such shares or units may be vested, unvested, or partially vested.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

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- Definition

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

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- Definition

Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

+ References

No definition available.

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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

The highest percentage of annual salary that an employee is permitted to utilize with respect to the plan.

+ References

+ Details

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- Definition

Number of shares purchased for issuance under share-based payment arrangement.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

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