Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014
Operating Revenues:
Transportation	$ 289.6	$ 304.3
Parking and lending	2.8	9.2
Storage	19.3	28.8
Other	18.0	14.6
Total operating revenues	329.7	356.9
Operating Costs and Expenses:
Fuel and transportation	27.0	33.0
Operation and maintenance	42.4	42.7
Administrative and general	30.6	26.8
Other operating costs and expenses	106.9	101.8
Total operating costs and expenses	206.9	204.3
Operating (loss) income	122.8	152.6
Other Deductions (Income):
Interest expense	45.2	40.9
Interest expense - affiliates	0	0
Interest income	(0.1)	(0.1)
Equity in earnings of subsidiaries	0	0
Equity losses in unconsolidated affiliates	0	86.1
Miscellaneous other income, net	(0.2)	(0.1)
Total other deductions	44.9	126.8
Income (loss) before income taxes	77.9	25.8
Income taxes	0.2	0.2
Net income (loss)	77.7	25.6
Net loss attributable to noncontrolling interests	0	(84.6)
Net income (loss) attributable to controlling interests	77.7	110.2
Eliminations
Operating Revenues:
Transportation	(22.0)	(22.8)
Parking and lending	0	0
Storage	0	0
Other	0	0
Total operating revenues	(22.0)	(22.8)
Operating Costs and Expenses:
Fuel and transportation	(22.0)	(22.8)
Operation and maintenance	0	0
Administrative and general	0	0
Other operating costs and expenses	0	0
Total operating costs and expenses	(22.0)	(22.8)
Operating (loss) income	0	0
Other Deductions (Income):
Interest expense	0	0
Interest expense - affiliates	0	0
Interest income	0	0
Equity in earnings of subsidiaries	175.4	233.7
Equity losses in unconsolidated affiliates		0
Miscellaneous other income, net	0	0
Total other deductions	175.4	233.7
Income (loss) before income taxes	(175.4)	(233.7)
Income taxes	0	0
Net income (loss)	(175.4)	(233.7)
Net loss attributable to noncontrolling interests		0
Net income (loss) attributable to controlling interests	(175.4)	(233.7)
Parent Guarantor | Reportable Legal Entities [Member]
Operating Revenues:
Transportation	0	0
Parking and lending	0	0
Storage	0	0
Other	0	0
Total operating revenues	0	0
Operating Costs and Expenses:
Fuel and transportation	0	0
Operation and maintenance	0	0
Administrative and general	0	(0.1)
Other operating costs and expenses	0	0.1
Total operating costs and expenses	0	0
Operating (loss) income	0	0
Other Deductions (Income):
Interest expense	0	0
Interest income - affiliates	(6.7)	(7.8)
Interest income	0	0
Equity in earnings of subsidiaries	(71.0)	(102.4)
Equity losses in unconsolidated affiliates		0
Miscellaneous other income, net	0	0
Total other deductions	(77.7)	(110.2)
Income (loss) before income taxes	77.7	110.2
Income taxes	0	0
Net income (loss)	77.7	110.2
Net loss attributable to noncontrolling interests		0
Net income (loss) attributable to controlling interests	77.7	110.2
Subsidiary Issuer | Reportable Legal Entities [Member]
Operating Revenues:
Transportation	0	0
Parking and lending	0	0
Storage	0	0
Other	0	0
Total operating revenues	0	0
Operating Costs and Expenses:
Fuel and transportation	0	0
Operation and maintenance	0	0
Administrative and general	0	0
Other operating costs and expenses	0	0
Total operating costs and expenses	0	0
Operating (loss) income	0	0
Other Deductions (Income):
Interest expense	23.9	18.7
Interest expense - affiliates	9.5	10.2
Interest income	0	0
Equity in earnings of subsidiaries	(104.4)	(131.3)
Equity losses in unconsolidated affiliates		0
Miscellaneous other income, net	0	0
Total other deductions	(71.0)	(102.4)
Income (loss) before income taxes	71.0	102.4
Income taxes	0	0
Net income (loss)	71.0	102.4
Net loss attributable to noncontrolling interests		0
Net income (loss) attributable to controlling interests	71.0	102.4
Non-Guarantor Subsidiaries | Reportable Legal Entities [Member]
Operating Revenues:
Transportation	311.6	327.1
Parking and lending	2.8	9.2
Storage	19.3	28.8
Other	18.0	14.6
Total operating revenues	351.7	379.7
Operating Costs and Expenses:
Fuel and transportation	49.0	55.8
Operation and maintenance	42.4	42.7
Administrative and general	30.6	26.9
Other operating costs and expenses	106.9	101.7
Total operating costs and expenses	228.9	227.1
Operating (loss) income	122.8	152.6
Other Deductions (Income):
Interest expense	21.3	22.2
Interest income - affiliates	(2.8)	(2.4)
Interest income	(0.1)	(0.1)
Equity in earnings of subsidiaries	0	0
Equity losses in unconsolidated affiliates		86.1
Miscellaneous other income, net	(0.2)	(0.1)
Total other deductions	18.2	105.7
Income (loss) before income taxes	104.6	46.9
Income taxes	0.2	0.2
Net income (loss)	104.4	46.7
Net loss attributable to noncontrolling interests		(84.6)
Net income (loss) attributable to controlling interests	$ 104.4	$ 131.3