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, 2013	Mar. 31, 2012
Operating Revenues [Abstract]
Transportation	$ 284.1	$ 287.5
Parking and lending	7.9	4.0
Storage	28.1	19.8
Other	8.4	1.6
Total operating revenues	328.5	312.9
Operating Costs and Expenses [Abstract]
Fuel and gas transportation	22.7	18.7
Operation and maintenance	40.2	37.6
Administrative and general	31.4	34.2
Other operating costs and expenses	92.5	88.8
Total operating costs and expenses	186.8	179.3
Operating Income	141.7	133.6
Other Deductions (Income):
Interest expense	40.5	39.0
Interest expense, affiliate, net	0	2.0
Interest income	(0.2)	(0.1)
Equity in earnings of subsidiaries	0	0
Miscellaneous other income, net	(0.2)	(0.1)
Total other deductions	40.1	40.8
Income before income taxes	101.6	92.8
Income taxes	0.2	0.2
Net Income	101.4	92.6
Parent Guarantor [Member]
Operating Revenues [Abstract]
Transportation	0	0
Parking and lending	0	0
Storage	0	0
Other	0	0
Total operating revenues	0	0
Operating Costs and Expenses [Abstract]
Fuel and gas 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 Income	0	0
Other Deductions (Income):
Interest expense	0	0
Interest expense, affiliate, net	(8.4)	(9.2)
Interest income	0	0
Equity in earnings of subsidiaries	(93.0)	(83.4)
Miscellaneous other income, net	0	0
Total other deductions	(101.4)	(92.6)
Income before income taxes	101.4	92.6
Income taxes	0	0
Net Income	101.4	92.6
Subsidiary Issuer [Member]
Operating Revenues [Abstract]
Transportation	0	0
Parking and lending	0	0
Storage	0	0
Other	0	0
Total operating revenues	0	0
Operating Costs and Expenses [Abstract]
Fuel and gas 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 Income	0	0
Other Deductions (Income):
Interest expense	17.2	15.9
Interest expense, affiliate, net	10.3	13.6
Interest income	0	0
Equity in earnings of subsidiaries	(120.5)	(112.9)
Miscellaneous other income, net	0	0
Total other deductions	(93.0)	(83.4)
Income before income taxes	93.0	83.4
Income taxes	0	0
Net Income	93.0	83.4
Non-Guarantor Subsidiaries [Member]
Operating Revenues [Abstract]
Transportation	305.8	309.3
Parking and lending	7.9	4.0
Storage	28.2	19.8
Other	8.4	1.6
Total operating revenues	350.3	334.7
Operating Costs and Expenses [Abstract]
Fuel and gas transportation	44.5	40.5
Operation and maintenance	40.2	37.6
Administrative and general	31.4	34.2
Other operating costs and expenses	92.5	88.8
Total operating costs and expenses	208.6	201.1
Operating Income	141.7	133.6
Other Deductions (Income):
Interest expense	23.3	23.1
Interest expense, affiliate, net	(1.9)	(2.4)
Interest income	(0.2)	(0.1)
Equity in earnings of subsidiaries	0	0
Miscellaneous other income, net	(0.2)	(0.1)
Total other deductions	21.0	20.5
Income before income taxes	120.7	113.1
Income taxes	0.2	0.2
Net Income	120.5	112.9
Consolidation, Eliminations [Member]
Operating Revenues [Abstract]
Transportation	(21.7)	(21.8)
Parking and lending	0	0
Storage	(0.1)	0
Other	0	0
Total operating revenues	(21.8)	(21.8)
Operating Costs and Expenses [Abstract]
Fuel and gas transportation	(21.8)	(21.8)
Operation and maintenance	0	0
Administrative and general	0	0
Other operating costs and expenses	0	0
Total operating costs and expenses	(21.8)	(21.8)
Operating Income	0	0
Other Deductions (Income):
Interest expense	0	0
Interest expense, affiliate, net	0	0
Interest income	0	0
Equity in earnings of subsidiaries	213.5	196.3
Miscellaneous other income, net	0	0
Total other deductions	213.5	196.3
Income before income taxes	(213.5)	(196.3)
Income taxes	0	0
Net Income	$ (213.5)	$ (196.3)