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Fair Values (fair value of the Level 3 financial Liabilities) (Details) - Designated as Hedging Instrument [Member] $ in Millions	12 Months Ended
	Dec. 31, 2018 CAD ($)
Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	$ 183
Total realized and unrealized gains (losses) included in non-regulated operating revenues	123
Net transfers out of Level 3	0
Ending Balance	306
Regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Non-regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Oil Financial Derivatives [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Total realized and unrealized gains (losses) included in non-regulated operating revenues	0
Net transfers out of Level 3	0
Ending Balance	0
Oil Financial Derivatives [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0
Oil Financial Derivatives [Member] | Regulated fuel for generation and purchased power [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Oil Financial Derivatives [Member] | Non-regulated fuel for generation and purchased power [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Regulatory Deferral Hedge [Member] | Physical natural gas purchases and sales [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	0
Total realized and unrealized gains (losses) included in non-regulated operating revenues	0
Net transfers out of Level 3	0
Ending Balance	0
Regulatory Deferral Hedge [Member] | Physical natural gas purchases and sales [Member] | Regulated fuel for generation and purchased power [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Regulatory Deferral Hedge [Member] | Physical natural gas purchases and sales [Member] | Non-regulated fuel for generation and purchased power [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Cash Flow Hedging And Held for Trading Hedge [Member] | Natural Gas [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	187
Total realized and unrealized gains (losses) included in non-regulated operating revenues	118
Net transfers out of Level 3	0
Ending Balance	305
Cash Flow Hedging And Held for Trading Hedge [Member] | Natural Gas [Member] | Regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Cash Flow Hedging And Held for Trading Hedge [Member] | Natural Gas [Member] | Non-regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Cash Flow Hedging And Held for Trading Hedge [Member] | Power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Beginning Balance	(4)
Total realized and unrealized gains (losses) included in non-regulated operating revenues	5
Net transfers out of Level 3	0
Ending Balance	1
Cash Flow Hedging And Held for Trading Hedge [Member] | Power [Member] | Regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	0
Cash Flow Hedging And Held for Trading Hedge [Member] | Power [Member] | Non-regulated fuel for generation and purchased power [Member] | Derivative Financial Instruments, Liabilities [Member]
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Increase (reduction) in benefit included in regulated and nonregulated fuel for generation and purchased power	$ 0

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 liabilities) related to those liabilities still held at the reporting date for which fair value is measured on a recurring basis using significant unobservable inputs (Level 3).

+ References

No definition available.

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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

No definition available.

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- Definition

Amount of gain (loss) recognized on the income statement for financial instrument classified as a liability 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)(1)
-URI http://asc.fasb.org/extlink&oid=66048111&loc=d3e19207-110258

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- Definition

Amount of transfers of financial instrument classified as a liability into (out of) level 3 of the fair value hierarchy.

+ References

No definition available.

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- Definition

Fair value of financial instrument classified as a liability 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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