Earnings per share (Details) (CAD) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Earnings per share [Abstract]
Basic earnings per share (in dollars per share)	5.45	4.51	3.95
Diluted earnings per share (in dollars per share)	5.41	4.48	3.92
Reconciliation between basic and diluted earnings per share:[Abstract]
Net income	2,457	2,104	1,854
Weighted-average shares outstanding (in shares)	451.1	466.3	469.2
Effect of stock options (in shares)	3.3	3.8	4.3
Weighted-average diluted shares outstanding (in shares)	454.4	470.1	473.5
Weighted-average number of stock options not included in the calculation of diluted earnings per share (in shares)	0.1	0	0.4

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

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-Name Accounting Standards Codification

-Glossary Antidilution

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-Glossary Diluted Earnings Per Share

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-Glossary Contingent Stock Agreement

-URI http://asc.fasb.org/extlink&oid=6508534

+ Details

- Definition

The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period.

+ References

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-Topic 260

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+ Details

- Definition

The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period.

+ References+ Details

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

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-Glossary Other Comprehensive Income

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-Glossary Net Income

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+ Details

- Definition

The average number of shares or units issued and outstanding that are used in calculating diluted EPS or earnings per unit (EPU), determined based on the timing of issuance of shares or units in the period.

+ References+ Details

- Definition

Number of [basic] shares or units, after adjustment for contingently issuable shares or units and other shares or units not deemed outstanding, determined by relating the portion of time within a reporting period that common shares or units have been outstanding to the total time in that period.

+ References

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