CONSOLIDATED STATEMENTS OF INCOME - USD ($) shares in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Operating Revenues:
Transportation	$ 1,180.7	$ 1,142.4	$ 1,091.1
Parking and lending	20.2	18.2	11.4
Storage	81.5	91.4	81.3
Other	40.2	55.2	65.4
Total operating revenues	1,322.6	1,307.2	1,249.2
Operating Costs and Expenses:
Fuel and transportation	54.8	70.8	99.3
Operation and maintenance	204.2	199.9	209.5
Administrative and general	126.5	142.2	130.4
Depreciation and amortization	322.8	317.8	323.7
Loss (gain) on sale of assets and impairments	49.0	3.7	(0.1)
Taxes other than income taxes	98.8	95.3	90.6
Total operating costs and expenses	856.1	829.7	853.4
Operating income	466.5	477.5	395.8
Other Deductions (Income):
Interest expense	171.0	182.8	176.4
Interest income	(0.4)	(0.4)	(0.4)
Miscellaneous other income, net	(2.1)	(7.7)	(2.7)
Total other deductions	168.5	174.7	173.3
Income before income taxes	298.0	302.8	222.5
Income taxes	1.0	0.6	0.5
Net income	$ 297.0	$ 302.2	$ 222.0
Net Income per Unit:
Net income per common unit (in dollars per unit)	$ 1.16	$ 1.18	$ 0.87
Weighted-average number of common units outstanding (in units)	250.3	250.3	248.8
Cash distribution declared and paid to common units per common unit (in dollars per unit)	$ 0.40	$ 0.40	$ 0.40