Debt - Commercial Paper Program (Details) $ in Millions	3 Months Ended
	Sep. 30, 2016 CAD	Sep. 30, 2016 USD ($)	Jun. 28, 2016 USD ($)	Dec. 31, 2015 CAD
Cash and Cash Equivalents [Line Items]
Short-term Debt, Weighted Average Interest Rate	0.75%	0.75%
Commercial Paper [Member]
Cash and Cash Equivalents [Line Items]
Line of Credit Facility, Current Borrowing Capacity			$ 1,000
Long-term Debt, Current Maturities	CAD 367,000,000	$ 280		CAD 0
Debt instrument maturity	less than 90 days
One Year Plus One Year Term Out Portion [Member]
Cash and Cash Equivalents [Line Items]
Line of Credit Facility, Current Borrowing Capacity			$ 1,000