Net Earnings per Common Unit (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net earnings per limited partner common unit
Net earnings	$ 28.8	$ 69.4	$ 165.2	$ 227.7
Weighted-average Common Units outstanding	18,500,000	18,500,000	18,500,000	18,500,000
Net earnings per Common Unit (in dollars per unit)	$ 1.04	$ 2.23	$ 5.71	$ 7.57
Dilutive TNCLP units outstanding	0	0	0	0
General Partner
Net earnings per limited partner common unit
Net earnings	$ 9.3	$ 27.5	$ 58.0	$ 85.5
Less: Net earnings allocable to General Partner	9.3	27.5	58.0	85.5
Common Units | Class B Common Units
Net earnings per limited partner common unit
Net earnings	0.3	0.7	1.6	2.2
Net earnings allocated	0.3	0.7	1.6	2.2
Common Units | Common Units
Net earnings per limited partner common unit
Net earnings	19.2	41.2	105.6	140.0
Net earnings allocated	$ 19.2	$ 41.2	$ 105.6	$ 140.0