Net Earnings per Common Unit (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Net earnings per limited partner common unit
Net earnings	$ 99.3	$ 100.1	$ 158.3	$ 203.0
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)	$ 3.31	$ 3.16	$ 5.34	$ 6.42
Dilutive TNCLP units outstanding	0	0	0	0
General Partner
Net earnings per limited partner common unit
Net earnings	$ 37.1	$ 40.7	$ 58.0	$ 82.2
Less: Net earnings allocable to General Partner	37.1	40.7	58.0	82.2
Common Units | Class B Common Units
Net earnings per limited partner common unit
Net earnings	0.9	1.0	1.5	2.0
Net earnings allocated	0.9	1.0	1.5	2.0
Common Units | Common Units
Net earnings per limited partner common unit
Net earnings	61.3	58.4	98.8	118.8
Net earnings allocated	$ 61.3	$ 58.4	$ 98.8	$ 118.8