Net Earnings per Common Unit (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Net earnings per limited partner common unit
Net earnings	$ 98.7	$ 99.3	$ 136.4	$ 158.3
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)	$ 3.22	$ 3.31	$ 4.66	$ 5.34
Dilutive TNCLP units outstanding	0	0	0	0
General Partner
Net earnings per limited partner common unit
Net earnings	$ 38.1	$ 37.1	$ 48.7	$ 58.0
Less: Net earnings allocable to General Partner	38.1	37.1	48.7	58.0
Common Units | Class B Common Units
Net earnings per limited partner common unit
Net earnings	0.9	0.9	1.3	1.5
Net earnings allocated	0.9	0.9	1.3	1.5
Common Units | Common Units
Net earnings per limited partner common unit
Net earnings	59.7	61.3	86.4	98.8
Net earnings allocated	$ 59.7	$ 61.3	$ 86.4	$ 98.8