The increase during the period in capital lease obligations due to entering into new capital leases.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

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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.

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The net cash inflow or cash outflow from issuing (borrowing) and repaying commercial paper.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 9
-Subparagraph c
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3098-108585

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The cash outflow associated with security instruments that either represent a creditor or an ownership relationship with the holder of the investment security with a maturity of beyond one year or normal operating cycle, if longer. Includes repayments of (a) debt, (b) capital lease obligations, (c) mandatory redeemable capital securities, and (d) any combination of (a), (b), or (c).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 15
-Subparagraph (a),(b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3291-108585

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Debt - Borrowings and Repayments (Detail) $ in Millions, $ in Millions	3 Months Ended
	Mar. 31, 2019 CAD ($)	Mar. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Debt
Debt repayments		$ 56	$ 80
Net commercial paper borrowings		357	$ 471
Revolving Credit Facility [Member]
Debt
Debt repayments	$ 15	11
Commercial Paper Program [Member]
Debt
Net commercial paper borrowings		357
Tax Exempt Bonds [Member]
Debt
Debt repayments		34
Financing leases and other debt [Member]
Debt
Debt repayments		11
Non-cash financing lease incurred		$ 30