Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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Sum of the carrying values as of the balance sheet date of all debt, including all short-term borrowings, long-term debt, and capital lease obligations.

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Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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Percentage points added to the reference rate to compute the variable rate on the debt instrument.

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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.

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The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Maximum borrowing capacity under the credit facility without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

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The portion of the carrying amount of long-term borrowings outstanding as of the balance sheet date, including current maturities, which accrues interest at a rate subject to change from time to time.

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Represent debt with interest rate periods that expire within the next 12 months.

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Maximum borrowing capacity under a term loan without consideration of any current restrictions on the amount that could be borrowed or the amounts currently outstanding under the facility.

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Debt - Classification and Utilization (Detail) CAD in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017 CAD	Dec. 31, 2017 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2016 USD ($)
Debt
Current portion of long-term debt		$ 739		$ 417
Debt and capital lease obligations		9,491		9,310
Carrying value of debt		9,491		9,310
Commercial Paper Program [Member]
Debt
Current portion of long-term debt		515
Maximum capacity		1,500
Debt and capital lease obligations		515
Debt term	397 days
Commercial paper, borrowings		515
Carrying value of debt		515
Tax Exempt Bonds [Member]
Debt
Current portion of long-term debt		167
Debt with interest rate periods that expiring in the next 12 months		831
Variable-rate tax-exempt bonds		328
Debt and capital lease obligations		2,352		2,304
Carrying value of debt		2,352		2,304
Revolving Credit Facility [Member]
Debt
Letters of credit outstanding		642
Maximum capacity		2,250		2,250
Debt and capital lease obligations				426
Unused and available credit capacity		1,093
Outstanding borrowings under credit facility		0
Carrying value of debt				426
Canadian Term Loan and Revolving Credit Facility [Member]
Debt
Letters of credit outstanding \| CAD	CAD 0		CAD 0
Debt and capital lease obligations		113		239
Outstanding borrowings under credit facility \| CAD	0		0
Carrying value of debt		113		239
Canadian Revolving Credit Facility [Member]
Debt
Maximum capacity \| CAD	50
Canadian Term Loan [Member]
Debt
Debt and capital lease obligations	142	113	321	239
Maximum term credit \| CAD	460
Carrying value of debt	CAD 142	113	CAD 321	239
Other Letter of Credit Facilities [Member]
Debt
Letters of credit outstanding		507		492
Capital Leases and Other [Member]
Debt
Debt and capital lease obligations		327		308
Carrying value of debt		327		$ 308
Other Debt [Member]
Debt
Current portion of long-term debt		$ 224
London Interbank Offered Rate [Member] \| Revolving Credit Facility [Member] \| Minimum [Member]
Debt
Spread rate	0.805%
London Interbank Offered Rate [Member] \| Revolving Credit Facility [Member] \| Maximum [Member]
Debt
Spread rate	1.30%
London Interbank Offered Rate [Member] \| Canadian Term Loan and Revolving Credit Facility [Member] \| Minimum [Member]
Debt
Spread rate	0.875%
London Interbank Offered Rate [Member] \| Canadian Term Loan and Revolving Credit Facility [Member] \| Maximum [Member]
Debt
Spread rate	1.50%