Share Capital (Share Trusts) (Details) - CAD ($) $ / shares in Units, shares in Millions, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Share Purchases by Share Trusts [Abstract]
Amount of purchase	$ 14	$ 33	$ 38
Share Settlements by Share Trusts [Abstract]
Share settlements by Share Trusts	$ 62	$ 45	$ 31
Share Units Plan [Member]
Share Purchases by Share Trusts [Abstract]
Share purchases by Share Trusts (in shares)	0.0	0.0	0.4
Weighted-average price per share (in dollars per share)	$ 0	$ 0	$ 104.87
Amount of purchase	$ 0	$ 0	$ 38
Share Settlements by Share Trusts [Abstract]
Number of common shares (in shares)	0.4	0.5	0.4
Weighted-average price per share (in dollars per share)	$ 88.23	$ 88.23	$ 84.53
Share settlements by Share Trusts	$ 35	$ 45	$ 31
Employee Share Investment Plan [Member]
Share Purchases by Share Trusts [Abstract]
Weighted-average price per share (in dollars per share)	$ 123.03	$ 118.83
Amount of purchase	$ 14	$ 33
Number of shares purchased on behalf of employees (in shares)	0.1	0.3
Share Settlements by Share Trusts [Abstract]
Number of common shares (in shares)	0.2	0.0
Weighted-average price per share (in dollars per share)	$ 118.04	$ 0
Share settlements by Share Trusts	$ 27	$ 0

Weighted-average price per share disbursed Share Trusts.

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Number of shares settled by Share trusts

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Share-Based Compensation Arrangement By Share-Based Payment Award, Shares Purchased For Award, Employer Match

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Amount of common shares settled by Share Trusts (value)

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Per share weighted-average price paid for shares purchased on open market for issuance under share-based payment arrangement.

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

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Equity impact of the value of stock that has been repurchased during the period and has not been retired and is not held in treasury. Some state laws may mandate the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

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