Net Earnings per Common Unit (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Net earnings per limited partner common unit
Net earnings	$ 69.4	$ 72.0	$ 227.7	$ 275.0
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)	$ 2.23	$ 2.60	$ 7.57	$ 9.02
Dilutive TNCLP units outstanding	0	0	0	0
General Partner
Net earnings per limited partner common unit
Net earnings	$ 27.5	$ 23.3	$ 85.5	$ 105.5
Less: Net earnings allocable to General Partner	27.5	23.3	85.5	105.5
Common Units | Class B Common Units
Net earnings per limited partner common unit
Net earnings	0.7	0.7	2.2	2.7
Net earnings allocated	0.7	0.7	2.2	2.7
Common Units | Common Units
Net earnings per limited partner common unit
Net earnings	41.2	48.0	140.0	166.8
Net earnings allocated	$ 41.2	$ 48.0	$ 140.0	$ 166.8