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Derivatives Instruments (Derivative Cash Flow Hedges Recorded in Income and AOCI and Notional Volumes of Outstanding Derivatives Designated as Cash Flow Hedges) (Details) $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2020 CAD ($)	Dec. 31, 2019 CAD ($)	Dec. 31, 2020 USD ($)
Cash Flow Hedges
Notional volumes of outstanding derivatives designated as cash flow hedges that are expected to settle			$ 100
Foreign exchange forwards
Cash Flow Hedges
Total gains (losses) in net income	$ 13	$ 0
Cash flow hedges
Cash Flow Hedges
Unrealized losses currently in AOCI to be reclassified into net income within the next twelve months	1
Cash flow hedges | Interest rate swaps
Cash Flow Hedges
Total gains (losses) in net income	0
Total unrealized gain (loss) in AOCI - effective portion, net of tax	1
Cash flow hedges | Interest rate swaps | Regulated
Cash Flow Hedges
Total gains (losses) in net income	0
Cash flow hedges | Interest rate swaps | Power | Non-Regulated
Cash Flow Hedges
Total unrealized gain (loss) in AOCI - effective portion, net of tax	0
Cash flow hedges | Foreign exchange forwards
Cash Flow Hedges
Total gains (losses) in net income	(2)	(3)
Total unrealized gain (loss) in AOCI - effective portion, net of tax	0	(1)
Cash flow hedges | Foreign exchange forwards | 2021
Cash Flow Hedges
Notional volumes of outstanding derivatives designated as cash flow hedges that are expected to settle			$ 350
Cash flow hedges | Foreign exchange forwards | Non-Regulated
Cash Flow Hedges
Total gains (losses) in net income	0	0
Cash flow hedges | Foreign exchange forwards | Regulated
Cash Flow Hedges
Total gains (losses) in net income	$ (2)	$ (3)

X

- Definition

Amount, after tax, of accumulated gain (loss) on derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
-Paragraph 11
-URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e637-108580

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- Definition

The estimated net amount of existing gains or losses on cash flow hedges at the reporting date expected to be reclassified to earnings within the next 12 months.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 30
-Section 50
-Paragraph 1
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Amount of increase (decrease) in the fair value of derivatives recognized in the income statement.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4A
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Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
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