Long-Term Debt - TH Facility (Details) $ in Millions	9 Months Ended
	Sep. 30, 2020 USD ($)	Sep. 30, 2020 CAD ($)	Dec. 31, 2019 USD ($)
Line of Credit Facility [Line Items]
Amount outstanding	$ 12,378		$ 11,833
TH Facility
Line of Credit Facility [Line Items]
Maximum borrowing capacity		$ 225,000,000
Remaining borrowing capacity		125,000,000
Amount outstanding		$ 224,000,000
Weighted average interest rate	1.88%	1.88%
TH Facility | Canadian Bankers' Acceptance Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	1.40%
TH Facility | Prime Rate
Line of Credit Facility [Line Items]
Basis spread on variable rate	0.40%