Guarantee of Securities of Subsidiaries Balance Sheets (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013	Dec. 31, 2012
Assets
Cash and cash equivalents	$ 12.1	$ 28.5	$ 4.3	$ 3.9
Receivables	124.3	119.2
Receivables - affiliate	3.5	1.1
Gas and liquids stored underground	2.1	0.7
Prepayments	10.2	12.9
Advances to affiliates	0	0
Other current assets	13.8	14.7
Total current assets	166.0	177.1
Investment in consolidated subsidiaries	0	0
Property, plant and equipment, gross	8,770.4	8,723.3
Less—accumulated depreciation and amortization	1,556.0	1,489.2
Property, plant and equipment, net	7,214.4	7,234.1
Other noncurrent assets	427.3	424.7
Advances to affiliates - noncurrent	0	0
Investment in unconsolidated affiliates	1.8	78.6
Total other assets	429.1	503.3
Total Assets	7,809.5	7,914.5
Liabilities and Equity
Payables	49.7	70.8
Payable to affiliates	1.9	1.2
Advances from affiliates	0	0
Other current liabilities	127.1	164.0
Total current liabilities	178.7	236.0
Total long-term debt and capital lease obligation	3,374.8	3,424.4
Payable to affiliate - noncurrent	16.0	16.0
Advances from affiliates - noncurrent	0	0
Other noncurrent liabilities	177.0	174.7
Total other liabilities and deferred credits	193.0	190.7
Total partners' capital/member's equity	4,060.4	3,976.9
Noncontrolling interest	2.6	86.5
Total Equity	4,063.0	4,063.4	3,844.1	3,877.1
Total Liabilities and Equity	7,809.5	7,914.5
Parent Guarantor
Assets
Cash and cash equivalents	0.1	0.2	0	0.1
Receivables	0	0
Receivables - affiliate	1.5	0.1
Gas and liquids stored underground	0	0
Prepayments	0.7	0.3
Advances to affiliates	0	0
Other current assets	0.1	0
Total current assets	2.4	0.6
Investment in consolidated subsidiaries	1,581.3	1,480.8
Property, plant and equipment, gross	0.6	0.6
Less—accumulated depreciation and amortization	0.6	0.6
Property, plant and equipment, net	0	0
Other noncurrent assets	0.3	0.3
Advances to affiliates - noncurrent	2,493.4	2,512.1
Investment in unconsolidated affiliates	0	0
Total other assets	2,493.7	2,512.4
Total Assets	4,077.4	3,993.8
Liabilities and Equity
Payables	0.3	0.2
Payable to affiliates	0.7	0.7
Advances from affiliates	0	0
Other current liabilities	0	0
Total current liabilities	1.0	0.9
Total long-term debt and capital lease obligation	0	0
Payable to affiliate - noncurrent	16.0	16.0
Advances from affiliates - noncurrent	0	0
Other noncurrent liabilities	0	0
Total other liabilities and deferred credits	16.0	16.0
Total partners' capital/member's equity	4,060.4	3,976.9
Noncontrolling interest	0	0
Total Equity	4,060.4	3,976.9
Total Liabilities and Equity	4,077.4	3,993.8
Subsidiary Issuer
Assets
Cash and cash equivalents	5.2	9.2	2.0	1.0
Receivables	0	0
Receivables - affiliate	0	0.1
Gas and liquids stored underground	0	0
Prepayments	0	0
Advances to affiliates	0	0
Other current assets	0	0
Total current assets	5.2	9.3
Investment in consolidated subsidiaries	6,267.3	6,138.3
Property, plant and equipment, gross	0	0
Less—accumulated depreciation and amortization	0	0
Property, plant and equipment, net	0	0
Other noncurrent assets	3.5	3.7
Advances to affiliates - noncurrent	177.0	168.7
Investment in unconsolidated affiliates	0	0
Total other assets	180.5	172.4
Total Assets	6,453.0	6,320.0
Liabilities and Equity
Payables	0.1	0
Payable to affiliates	0	0
Advances from affiliates	189.5	194.4
Other current liabilities	14.2	19.7
Total current liabilities	203.8	214.1
Total long-term debt and capital lease obligation	1,380.1	1,379.9
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	3,287.8	3,245.2
Other noncurrent liabilities	0	0
Total other liabilities and deferred credits	3,287.8	3,245.2
Total partners' capital/member's equity	1,581.3	1,480.8
Noncontrolling interest	0	0
Total Equity	1,581.3	1,480.8
Total Liabilities and Equity	6,453.0	6,320.0
Non-Guarantor Subsidiaries
Assets
Cash and cash equivalents	6.8	19.1	2.3	2.8
Receivables	124.4	119.2
Receivables - affiliate	11.5	14.3
Gas and liquids stored underground	2.1	0.7
Prepayments	9.5	12.6
Advances to affiliates	189.5	194.4
Other current assets	16.3	23.8
Total current assets	360.1	384.1
Investment in consolidated subsidiaries	0	0
Property, plant and equipment, gross	8,769.8	8,722.7
Less—accumulated depreciation and amortization	1,555.4	1,488.6
Property, plant and equipment, net	7,214.4	7,234.1
Other noncurrent assets	423.6	420.7
Advances to affiliates - noncurrent	794.4	733.1
Investment in unconsolidated affiliates	1.8	78.6
Total other assets	1,219.8	1,232.4
Total Assets	8,794.3	8,850.6
Liabilities and Equity
Payables	49.4	70.6
Payable to affiliates	10.8	13.9
Advances from affiliates	0	0
Other current liabilities	115.4	153.3
Total current liabilities	175.6	237.8
Total long-term debt and capital lease obligation	1,994.7	2,044.5
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	177.0	168.7
Other noncurrent liabilities	177.1	174.8
Total other liabilities and deferred credits	354.1	343.5
Total partners' capital/member's equity	6,267.3	6,138.3
Noncontrolling interest	2.6	86.5
Total Equity	6,269.9	6,224.8
Total Liabilities and Equity	8,794.3	8,850.6
Eliminations
Assets
Cash and cash equivalents	0	0	0	0
Receivables	(0.1)	0
Receivables - affiliate	(9.5)	(13.4)
Gas and liquids stored underground	0	0
Prepayments	0	0
Advances to affiliates	(189.5)	(194.4)
Other current assets	(2.6)	(9.1)
Total current assets	(201.7)	(216.9)
Investment in consolidated subsidiaries	(7,848.6)	(7,619.1)
Property, plant and equipment, gross	0	0
Less—accumulated depreciation and amortization	0	0
Property, plant and equipment, net	0	0
Other noncurrent assets	(0.1)	0
Advances to affiliates - noncurrent	(3,464.8)	(3,413.9)
Investment in unconsolidated affiliates	0	0
Total other assets	(3,464.9)	(3,413.9)
Total Assets	(11,515.2)	(11,249.9)
Liabilities and Equity
Payables	(0.1)	0
Payable to affiliates	(9.6)	(13.4)
Advances from affiliates	(189.5)	(194.4)
Other current liabilities	(2.5)	(9.0)
Total current liabilities	(201.7)	(216.8)
Total long-term debt and capital lease obligation	0	0
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	(3,464.8)	(3,413.9)
Other noncurrent liabilities	(0.1)	(0.1)
Total other liabilities and deferred credits	(3,464.9)	(3,414.0)
Total partners' capital/member's equity	(7,848.6)	(7,619.1)
Noncontrolling interest	0	0
Total Equity	(7,848.6)	(7,619.1)
Total Liabilities and Equity	$ (11,515.2)	$ (11,249.9)