Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Operating Revenues:
Transportation	$ 293.3	$ 248.5	$ 599.7	$ 547.0
Storage, parking and lending	22.9	21.6	46.3	46.7
Other	11.1	15.2	27.2	27.0
Total operating revenues	327.3	285.3	673.2	620.7
Operating Costs and Expenses:
Fuel and transportation	4.2	4.1	6.8	8.5
Operation and maintenance	50.7	50.9	93.7	97.3
Administrative and general	37.0	35.7	70.2	67.8
Other operating costs and expenses	113.0	108.9	227.0	220.7
Total operating costs and expenses	204.9	199.6	397.7	394.3
Operating (loss) income	122.4	85.7	275.5	226.4
Other Deductions (Income):
Interest expense	45.5	43.3	90.8	87.4
Interest expense - affiliates, net	0.0	0.0	0.0	0.0
Interest income	0.0	(0.1)	(0.3)	(0.1)
Equity in earnings of subsidiaries	0.0	0.0	0.0	0.0
Miscellaneous other expense (income), net	1.1	0.2	0.9	(0.6)
Total other (income) deductions	46.6	43.4	91.4	86.7
Income (loss) before income taxes	75.8	42.3	184.1	139.7
Income taxes	0.1	0.1	0.3	0.3
Net income (loss)	75.7	42.2	183.8	139.4
Reportable Legal Entities | Parent Guarantor
Operating Revenues:
Transportation	0.0	0.0	0.0	0.0
Storage, parking and lending	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Total operating revenues	0.0	0.0	0.0	0.0
Operating Costs and Expenses:
Fuel and transportation	0.0	0.0	0.0	0.0
Operation and maintenance	0.0	0.0	0.0	0.0
Administrative and general	(0.1)	(0.1)	(0.1)	(0.1)
Other operating costs and expenses	0.1	0.2	0.2	0.2
Total operating costs and expenses	0.0	0.1	0.1	0.1
Operating (loss) income	0.0	(0.1)	(0.1)	(0.1)
Other Deductions (Income):
Interest expense	0.0	0.0	0.0	0.0
Interest income - affiliates, net	(18.3)	(17.5)	(37.3)	(31.8)
Interest income		0.0	0.0	0.0
Equity in earnings of subsidiaries	(57.4)	(24.8)	(146.6)	(107.7)
Miscellaneous other expense (income), net	0.0	0.0	0.0	0.0
Total other (income) deductions	(75.7)	(42.3)	(183.9)	(139.5)
Income (loss) before income taxes	75.7	42.2	183.8	139.4
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	75.7	42.2	183.8	139.4
Reportable Legal Entities | Subsidiary Issuer
Operating Revenues:
Transportation	0.0	0.0	0.0	0.0
Storage, parking and lending	0.0	0.0	0.0	0.0
Other	0.0	0.0	0.0	0.0
Total operating revenues	0.0	0.0	0.0	0.0
Operating Costs and Expenses:
Fuel and transportation	0.0	0.0	0.0	0.0
Operation and maintenance	0.0	0.0	0.0	0.0
Administrative and general	0.0	0.0	0.0	0.0
Other operating costs and expenses	0.0	0.0	0.0	0.0
Total operating costs and expenses	0.0	0.0	0.0	0.0
Operating (loss) income	0.0	0.0	0.0	0.0
Other Deductions (Income):
Interest expense	33.2	30.7	62.7	62.6
Interest expense - affiliates, net	15.2	13.3	34.3	24.1
Interest income		0.0	0.0	0.0
Equity in earnings of subsidiaries	(105.8)	(68.8)	(243.6)	(194.4)
Miscellaneous other expense (income), net	0.0	0.0	0.0	0.0
Total other (income) deductions	(57.4)	(24.8)	(146.6)	(107.7)
Income (loss) before income taxes	57.4	24.8	146.6	107.7
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	57.4	24.8	146.6	107.7
Reportable Legal Entities | Non-Guarantor Subsidiaries
Operating Revenues:
Transportation	314.1	268.9	640.7	588.2
Storage, parking and lending	23.0	21.6	46.9	47.0
Other	11.1	15.2	27.2	27.0
Total operating revenues	348.2	305.7	714.8	662.2
Operating Costs and Expenses:
Fuel and transportation	25.1	24.5	48.4	50.0
Operation and maintenance	50.7	50.9	93.7	97.3
Administrative and general	37.1	35.8	70.3	67.9
Other operating costs and expenses	112.9	108.7	226.8	220.5
Total operating costs and expenses	225.8	219.9	439.2	435.7
Operating (loss) income	122.4	85.8	275.6	226.5
Other Deductions (Income):
Interest expense	12.3	12.6	28.1	24.8
Interest expense - affiliates, net	3.1	4.2	3.0	7.7
Interest income		(0.1)	(0.3)	(0.1)
Equity in earnings of subsidiaries	0.0	0.0	0.0	0.0
Miscellaneous other expense (income), net	1.1	0.2	0.9	(0.6)
Total other (income) deductions	16.5	16.9	31.7	31.8
Income (loss) before income taxes	105.9	68.9	243.9	194.7
Income taxes	0.1	0.1	0.3	0.3
Net income (loss)	105.8	68.8	243.6	194.4
Eliminations
Operating Revenues:
Transportation	(20.8)	(20.4)	(41.0)	(41.2)
Storage, parking and lending	(0.1)	0.0	(0.6)	(0.3)
Other	0.0	0.0	0.0	0.0
Total operating revenues	(20.9)	(20.4)	(41.6)	(41.5)
Operating Costs and Expenses:
Fuel and transportation	(20.9)	(20.4)	(41.6)	(41.5)
Operation and maintenance	0.0	0.0	0.0	0.0
Administrative and general	0.0	0.0	0.0	0.0
Other operating costs and expenses	0.0	0.0	0.0	0.0
Total operating costs and expenses	(20.9)	(20.4)	(41.6)	(41.5)
Operating (loss) income	0.0	0.0	0.0	0.0
Other Deductions (Income):
Interest expense	0.0	0.0	0.0	0.0
Interest expense - affiliates, net	0.0	0.0	0.0	0.0
Interest income		0.0	0.0	0.0
Equity in earnings of subsidiaries	163.2	93.6	390.2	302.1
Miscellaneous other expense (income), net	0.0	0.0	0.0	0.0
Total other (income) deductions	163.2	93.6	390.2	302.1
Income (loss) before income taxes	(163.2)	(93.6)	(390.2)	(302.1)
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	$ (163.2)	$ (93.6)	$ (390.2)	$ (302.1)