Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Operating Revenues:
Transportation	$ 245.8	$ 266.4	$ 792.8	$ 852.0
Storage, parking and lending	21.1	23.2	67.8	79.8
Other	11.0	10.9	38.0	53.3
Total operating revenues	277.9	300.5	898.6	985.1
Operating Costs and Expenses:
Fuel and transportation	3.5	9.0	12.0	42.7
Operation and maintenance	46.9	49.0	144.2	141.0
Administrative and general	32.8	27.1	100.6	96.9
Other operating costs and expenses	113.9	105.4	334.6	363.5
Total operating costs and expenses	197.1	190.5	591.4	644.1
Operating (loss) income	80.8	110.0	307.2	341.0
Other Deductions (Income):
Interest expense	43.5	41.0	130.9	131.1
Interest expense - affiliates, net	0.0	0.0	0.0	0.0
Interest income	0.0	0.0	(0.1)	(0.3)
Equity in earnings of subsidiaries	0.0	0.0	0.0	0.0
Miscellaneous other income, net	(0.7)	(1.1)	(1.3)	(3.5)
Total other (income) deductions	42.8	39.9	129.5	127.3
Income (loss) before income taxes	38.0	70.1	177.7	213.7
Income taxes	0.1	0.3	0.4	0.9
Net income (loss)	37.9	69.8	177.3	212.8
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)	(0.3)	(0.2)	(0.3)
Other operating costs and expenses	0.1	0.4	0.3	0.5
Total operating costs and expenses	0.0	0.1	0.1	0.2
Operating (loss) income	0.0	(0.1)	(0.1)	(0.2)
Other Deductions (Income):
Interest expense	0.0	0.0	0.0	0.0
Interest income - affiliates, net	(17.5)	(12.4)	(49.3)	(34.6)
Interest income			0.0	0.0
Equity in earnings of subsidiaries	(20.4)	(57.5)	(128.1)	(178.4)
Miscellaneous other income, net	0.0	0.0	0.0	0.0
Total other (income) deductions	(37.9)	(69.9)	(177.4)	(213.0)
Income (loss) before income taxes	37.9	69.8	177.3	212.8
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	37.9	69.8	177.3	212.8
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
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	29.2	32.2	91.8	97.6
Interest expense - affiliates, net	14.0	11.0	38.1	30.1
Interest income			0.0	(0.2)
Equity in earnings of subsidiaries	(63.6)	(100.7)	(258.0)	(305.9)
Miscellaneous other income, net	0.0	0.0	0.0	0.0
Total other (income) deductions	(20.4)	(57.5)	(128.1)	(178.4)
Income (loss) before income taxes	20.4	57.5	128.1	178.4
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	20.4	57.5	128.1	178.4
Reportable Legal Entities | Non-Guarantor Subsidiaries
Operating Revenues:
Transportation	266.5	288.9	854.7	918.3
Storage, parking and lending	21.1	23.2	68.1	80.0
Other	11.0	10.9	38.0	53.3
Total operating revenues	298.6	323.0	960.8	1,051.6
Operating Costs and Expenses:
Fuel and transportation	24.2	31.5	74.2	109.2
Operation and maintenance	46.9	49.0	144.2	141.0
Administrative and general	32.9	27.4	100.8	97.2
Other operating costs and expenses	113.8	105.0	334.3	363.0
Total operating costs and expenses	217.8	212.9	653.5	710.4
Operating (loss) income	80.8	110.1	307.3	341.2
Other Deductions (Income):
Interest expense	14.3	8.8	39.1	33.5
Interest expense - affiliates, net	3.5	1.4	11.2	4.5
Interest income			(0.1)	(0.1)
Equity in earnings of subsidiaries	0.0	0.0	0.0	0.0
Miscellaneous other income, net	(0.7)	(1.1)	(1.3)	(3.5)
Total other (income) deductions	17.1	9.1	48.9	34.4
Income (loss) before income taxes	63.7	101.0	258.4	306.8
Income taxes	0.1	0.3	0.4	0.9
Net income (loss)	63.6	100.7	258.0	305.9
Eliminations
Operating Revenues:
Transportation	(20.7)	(22.5)	(61.9)	(66.3)
Storage, parking and lending	0.0	0.0	(0.3)	(0.2)
Other	0.0	0.0	0.0	0.0
Total operating revenues	(20.7)	(22.5)	(62.2)	(66.5)
Operating Costs and Expenses:
Fuel and transportation	(20.7)	(22.5)	(62.2)	(66.5)
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	(20.7)	(22.5)	(62.2)	(66.5)
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
Equity in earnings of subsidiaries	84.0	158.2	386.1	484.3
Miscellaneous other income, net	0.0	0.0	0.0	0.0
Total other (income) deductions	84.0	158.2	386.1	484.3
Income (loss) before income taxes	(84.0)	(158.2)	(386.1)	(484.3)
Income taxes	0.0	0.0	0.0	0.0
Net income (loss)	$ (84.0)	$ (158.2)	$ (386.1)	$ (484.3)