Face (par) amount of debt instrument at time of issuance.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 30
-Section 55
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- Definition

Effective interest rate for the funds borrowed under the debt agreement considering interest compounding and original issue discount or premium.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
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-Section S99
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Contractual interest rate for funds borrowed, under the debt agreement.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

Period of time between issuance and maturity of debt instrument, in PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

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- Definition

Nominal or face amount used to calculate payments on the derivative liability.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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- Definition

Difference between the fair value of payments made and the carrying amount of debt which is extinguished prior to maturity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The cash inflow during the period from additional borrowings in aggregate debt. Includes proceeds from short-term and long-term debt.

+ References

No definition available.

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The cash outflow during the period from the repayment of aggregate short-term and long-term debt and payment of capital lease obligations.

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No definition available.

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Debt - A (Narrative) (Details)	3 Months Ended				9 Months Ended		12 Months Ended
Debt - A (Narrative) (Details)	Sep. 30, 2015 CAD	Sep. 30, 2015 USD ($)	Mar. 31, 2015 CAD	Mar. 31, 2015 USD ($)	Sep. 30, 2015 CAD	Sep. 30, 2015 USD ($)	Dec. 31, 2014 CAD	Dec. 31, 2015	Sep. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)
Debt Instrument [Line Items]
Repayments of debt \| CAD							CAD 8,000,000
Notes Payable to Banks [Member] \| 2.900% 10-year Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount										$ 700,000,000
Interest rate			2.90%							2.90%
Debt instrument term			10 years	10 years
Proceeds from issuance of debt instrument			CAD 873,000,000	$ 694,000,000
Notional amount	CAD 700,000,000		CAD 700,000,000		CAD 700,000,000				$ 700,000,000	$ 700,000,000
Notes Payable to Banks [Member] \| 4.800% 30-year Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 550,000,000
Interest rate	4.80%				4.80%				4.80%
Debt instrument term	30 years	30 years
Notes Payable to Banks [Member] \| 3.700% 10.5-year Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 250,000,000
Interest rate	3.70%				3.70%				3.70%
Debt instrument term	10 years 6 months	10 years 6 months
Notes Payable to Banks [Member] \| 4.800% and 3.700% Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 800,000,000
Proceeds from issuance of debt instrument	CAD 1,032,000,000	$ 789,000,000
Notes Payable to Banks [Member] \| 6.125% 100-year Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 900,000,000
Interest rate	6.125%				6.125%			6.25%	6.125%
Debt instrument term	100 years	100 years
Notional amount									$ 700,000,000
Notes Payable to Banks [Member] \| 4.800% 20-year Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 300,000,000
Interest rate	4.80%				4.80%				4.80%
Debt instrument term	20 years	20 years
Notes Payable to Banks [Member] \| 6.25% and 4.800% Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount									$ 1,200,000,000
Proceeds from issuance of debt instrument					CAD 1,569,000,000	$ 1,186,000,000
Interest Rate Swap [Member]
Debt Instrument [Line Items]
Loss on extinguishment of debt	CAD 47,000,000	$ 36,000,000
Interest rate, effective percentage			3.61%							3.61%
Interest Rate Swap [Member] \| 2.900% 10-year Notes [Member]
Debt Instrument [Line Items]
Repayments of debt			CAD 63,000,000	$ 50,000,000