Draws on Credit Facility that are Designated as Net Investments in Foreign Operations (Parenthetical) (Detail) CAD in Millions, $ in Millions		Dec. 31, 2016 USD ($)	Dec. 31, 2016 CAD	Dec. 31, 2015 USD ($)
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Credit facility		$ 1,206		$ 1,291
Canadian Dollars
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Credit facility	[1]	34	CAD 46
Canadian Dollars | Not Designated as Hedging Instrument
Derivative Instruments And Hedging Activities Disclosures [Line Items]
Credit facility		$ 45

[1] We have drawn an additional $45 million on the credit facility in Canadian dollars that has not been designated as a hedging instrument.