CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 9.9	$ 3.9
Receivables:
Trade, net	83.0	105.3
Other	11.7	6.9
Gas transportation receivables	6.4	9.0
Costs recoverable from customers	2.7	3.3
Gas and liquids stored underground	1.6	10.8
Prepayments	18.3	15.2
Other current assets	5.6	2.6
Total current assets	139.2	157.0
Property, Plant and Equipment:
Natural gas transmission and other plant	8,351.9	8,165.3
Construction work in progress	170.7	258.0
Property, plant and equipment, gross	8,522.6	8,423.3
Less-accumulated depreciation and amortization	1,345.9	1,234.1
Property, plant and equipment, net	7,176.7	7,189.2
Other Assets:
Goodwill	267.0	267.0
Gas stored underground	103.4	109.7
Investment in unconsolidated affiliates	25.0	0
Other	135.6	139.6
Total other assets	531.0	516.3
Total Assets	7,846.9	7,862.5
Payables:
Trade	33.1	69.8
Affiliates	1.0	2.7
Other	15.5	19.2
Gas Payables:
Transportation	9.2	10.4
Storage	0.1	3.5
Accrued taxes, other	47.6	40.5
Accrued interest	47.5	42.5
Accrued payroll and employee benefits	14.2	25.2
Deferred income	6.6	19.9
Other current liabilities	24.1	22.1
Total current liabilities	198.9	255.8
Long-term debt	3,258.3	3,539.2
Other Liabilities and Deferred Credits:
Pension liability	26.9	26.8
Asset retirement obligation	35.4	33.2
Provision for other asset retirement	58.8	57.4
Payable to affiliate	16.0	16.0
Other	63.2	57.0
Total other liabilities and deferred credits	200.3	190.4
Commitments and Contingencies
Partners' Capital:
Common units - 220.4 million units and 207.7 million units issued and outstanding as of June 30, 2013 and December 31, 2012	3,476.5	3,190.3
Class B units - 22.9 million units issued and outstanding as of June 30, 2013 and December 31, 2012	678.3	678.3
General partner	81.6	75.8
Accumulated other comprehensive loss	(67.3)	(67.3)
Total partners' capital	4,169.1	3,877.1
Noncontrolling interest	20.3	0
Total Equity	4,189.4	3,877.1
Total Liabilities and Equity	$ 7,846.9	$ 7,862.5