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Fair Values (fair value of the Level 3 financial assets) (Details) - Designated as Hedging Instrument [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 CAD ($)
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 34
Total realized and unrealized gains (losses) included in non-regulated operating revenues	(13)
Ending Balance	21
Cash Flow Hedging And Held for Trading Hedge [Member] | Natural Gas [Member] | Derivative Financial Instruments, Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	25
Total realized and unrealized gains (losses) included in non-regulated operating revenues	(7)
Ending Balance	18
Cash Flow Hedging And Held for Trading Hedge [Member] | Power [Member] | Derivative Financial Instruments, Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	9
Total realized and unrealized gains (losses) included in non-regulated operating revenues	(6)
Ending Balance	$ 3

X

- Definition

Total amount of unrealized (holding) gain (loss) and realized gain (loss) which is included in the statement of income (or changes in net assets) related to those assets still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

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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

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- Definition

Fair value of financial instrument classified as an asset measured using unobservable inputs that reflect the entity's own assumption about the assumptions market participants would use in pricing.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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