Guarantee of Securities of Subsidiaries Guarantee of Securities of Subsidiaries Statements of Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Operating Revenues [Abstract]
Transportation	$ 242.3	$ 245.0	$ 526.4	$ 532.5
Parking and lending	7.1	7.8	15.0	11.8
Storage	27.4	18.9	55.5	38.7
Other	11.9	4.1	20.3	5.7
Total operating revenues	288.7	275.8	617.2	588.7
Operating Costs and Expenses [Abstract]
Fuel and transportation	27.4	15.0	50.1	33.7
Operation and maintenance	43.8	41.9	84.0	79.5
Administrative and general	28.9	25.2	60.3	59.4
Other operating costs and expenses	77.5	85.2	170.0	174.0
Total operating costs and expenses	177.6	167.3	364.4	346.6
Operating (loss) income	111.1	108.5	252.8	242.1
Other Deductions (Income):
Interest expense	40.7	41.5	81.2	80.5
Interest (income) expense, affiliate, net	0	2.0	0	4.0
Interest income	(0.1)	(0.1)	(0.3)	(0.2)
Equity in earnings of subsidiaries	0	0	0	0
Miscellaneous other income, net	0	(0.1)	(0.2)	(0.2)
Total other deductions	40.6	43.3	80.7	84.1
Income before income taxes	70.5	65.2	172.1	158.0
Income taxes	0.1	0.1	0.3	0.3
Net income (loss)	70.4	65.1	171.8	157.7
Net loss attributable to noncontrolling interests	(0.1)	0	(0.1)	0
Net income attributable to controlling interests	70.5	65.1	171.9	157.7
Parent Guarantor [Member]
Operating Revenues [Abstract]
Transportation	0	0	0	0
Parking and lending	0	0	0	0
Storage	0	0	0	0
Other	0	0	0	0
Total operating revenues	0	0	0	0
Operating Costs and Expenses [Abstract]
Fuel and transportation	0	0	0	0
Operation and maintenance	0	0	0	0
Administrative and general	0	(0.1)	0	(0.1)
Other operating costs and expenses	0.1	0.1	0.1	0.1
Total operating costs and expenses	0.1	0	0.1	0
Operating (loss) income	(0.1)	0	(0.1)	0
Other Deductions (Income):
Interest expense	0	0	0	0
Interest (income) expense, affiliate, net	(8.2)	(8.6)	(16.6)	(17.8)
Interest income	0	0	0	0
Equity in earnings of subsidiaries	(62.4)	(56.5)	(155.4)	(139.9)
Miscellaneous other income, net		0	0	0
Total other deductions	(70.6)	(65.1)	(172.0)	(157.7)
Income before income taxes	70.5	65.1	171.9	157.7
Income taxes	0	0	0	0
Net income (loss)	70.5	65.1	171.9	157.7
Net loss attributable to noncontrolling interests	0		0
Net income attributable to controlling interests	70.5		171.9
Subsidiary Issuer [Member]
Operating Revenues [Abstract]
Transportation	0	0	0	0
Parking and lending	0	0	0	0
Storage	0	0	0	0
Other	0	0	0	0
Total operating revenues	0	0	0	0
Operating Costs and Expenses [Abstract]
Fuel and transportation	0	0	0	0
Operation and maintenance	0.3	0	0.3	0
Administrative and general	0.8	0	0.8	0
Other operating costs and expenses	0.1	0	0.1	0
Total operating costs and expenses	1.2	0	1.2	0
Operating (loss) income	(1.2)	0	(1.2)	0
Other Deductions (Income):
Interest expense	18.0	15.8	35.2	31.7
Interest (income) expense, affiliate, net	10.2	13.8	20.5	27.4
Interest income	0	0	0	0
Equity in earnings of subsidiaries	(91.8)	(86.1)	(212.3)	(199.0)
Miscellaneous other income, net		0	0	0
Total other deductions	(63.6)	(56.5)	(156.6)	(139.9)
Income before income taxes	62.4	56.5	155.4	139.9
Income taxes	0	0	0	0
Net income (loss)	62.4	56.5	155.4	139.9
Net loss attributable to noncontrolling interests	0		0
Net income attributable to controlling interests	62.4		155.4
Non-Guarantor Subsidiaries [Member]
Operating Revenues [Abstract]
Transportation	264.6	266.6	570.4	575.9
Parking and lending	7.1	7.8	15.0	11.8
Storage	27.4	19.0	55.6	38.8
Other	11.9	4.1	20.3	5.7
Total operating revenues	311.0	297.5	661.3	632.2
Operating Costs and Expenses [Abstract]
Fuel and transportation	49.7	36.7	94.2	77.2
Operation and maintenance	43.5	41.9	83.7	79.5
Administrative and general	28.1	25.3	59.5	59.5
Other operating costs and expenses	77.3	85.1	169.8	173.9
Total operating costs and expenses	198.6	189.0	407.2	390.1
Operating (loss) income	112.4	108.5	254.1	242.1
Other Deductions (Income):
Interest expense	22.7	25.7	46.0	48.8
Interest (income) expense, affiliate, net	(2.0)	(3.2)	(3.9)	(5.6)
Interest income	(0.1)	(0.1)	(0.3)	(0.2)
Equity in earnings of subsidiaries	0	0	0	0
Miscellaneous other income, net		(0.1)	(0.2)	(0.2)
Total other deductions	20.6	22.3	41.6	42.8
Income before income taxes	91.8	86.2	212.5	199.3
Income taxes	0.1	0.1	0.3	0.3
Net income (loss)	91.7	86.1	212.2	199.0
Net loss attributable to noncontrolling interests	(0.1)		(0.1)
Net income attributable to controlling interests	91.8		212.3
Consolidation, Eliminations [Member]
Operating Revenues [Abstract]
Transportation	(22.3)	(21.6)	(44.0)	(43.4)
Parking and lending	0	0	0	0
Storage	0	(0.1)	(0.1)	(0.1)
Other	0	0	0	0
Total operating revenues	(22.3)	(21.7)	(44.1)	(43.5)
Operating Costs and Expenses [Abstract]
Fuel and transportation	(22.3)	(21.7)	(44.1)	(43.5)
Operation and maintenance	0	0	0	0
Administrative and general	0	0	0	0
Other operating costs and expenses	0	0	0	0
Total operating costs and expenses	(22.3)	(21.7)	(44.1)	(43.5)
Operating (loss) income	0	0	0	0
Other Deductions (Income):
Interest expense	0	0	0	0
Interest (income) expense, affiliate, net	0	0	0	0
Interest income	0	0	0	0
Equity in earnings of subsidiaries	154.2	142.6	367.7	338.9
Miscellaneous other income, net		0	0	0
Total other deductions	154.2	142.6	367.7	338.9
Income before income taxes	(154.2)	(142.6)	(367.7)	(338.9)
Income taxes	0	0	0	0
Net income (loss)	(154.2)	(142.6)	(367.7)	(338.9)
Net loss attributable to noncontrolling interests	0		0
Net income attributable to controlling interests	$ (154.2)		$ (367.7)