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employee future benefits - Assumptions (Details) - Pension plans - CAD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019
employee future benefits |  |
Discount rate used to determine net benefit costs | 3.10% | 3.90%
Discount rate used to determine defined benefit obligations | 2.50% | 3.10%
Discount rate used to determine current service cost in subsequent fiscal year | 2.70% | 3.20%
Rate of future increases in compensation used to determine net benefit costs | 2.90% | 2.80%
Rate of future increases in compensation used to defined benefit obligations | 2.90% | 2.90%
Increase in life expectancy in actuarial assumption | 1 year | 1 year
Decrease in actuarial assumption (as a per cent) | 0.25% | 0.25%
Life expectancy |  |
employee future benefits |  |
Effect of increase in actuarial assumption on obligation | $ 349 | $ 297
Effect of increase in actuarial assumption on expense | 11 | 9
Discount rate |  |
employee future benefits |  |
Effect of decrease in actuarial assumption on obligation | 386 | 342
Effect of decrease in actuarial assumption on expense | 15 | 13
Rate of future increases in compensation |  |
employee future benefits |  |
Effect of decrease in actuarial assumption on obligation | (36) | (32)
Effect of decrease in actuarial assumption on expense | $ (3) | $ (4)

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- Definition The discount rate used as the significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The expected rate of salary increases used as a significant actuarial assumption to determine the present value of a defined benefit obligation. [Refer: Defined benefit plans [member]; Defined benefit obligation, at present value; Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 144 -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_144&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The increase (decrease) in a defined benefit obligation that would have been caused by a decrease in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 145 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_145_a&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The increase (decrease) in a defined benefit obligation that would have been caused by an increase in a significant actuarial assumption that was reasonably possible at the end of the reporting period. [Refer: Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 145 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_145_a&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The reasonably possible percentage of the decrease in the actuarial assumption used to determine the present value of defined benefit obligation. [Refer: Actuarial assumptions [member]] + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Name IAS -Number 19 -IssueDate 2020-01-01 -Paragraph 145 -Subparagraph a -URI http://eifrs.ifrs.org/eifrs/xifrs-link?type=IAS&num=19&code=ifrs-tx-2020-en-r&anchor=para_145_a&doctype=Standard -URIDate 2020-01-01 + Details
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- Definition The discount rate used as the significant actuarial assumption to determine net benefit costs. + References No definition available. + Details
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- Definition The reasonably possible increase life expectancy in the actuarial assumption used to determine the present value of defined benefit obligation, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References No definition available. + Details
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