CONDENSED CONSOLIDATED BALANCE SHEETS (Unaudited) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012
Current Assets:
Cash and cash equivalents	$ 4.3	$ 3.9
Receivables:
Trade, net	102.1	105.3
Other	7.2	6.9
Gas transportation receivables	9.2	9.0
Costs recoverable from customers	2.4	3.3
Gas stored underground	0.9	7.0
Prepayments	11.7	15.2
Other current assets	2.4	2.6
Total current assets	140.2	153.2
Property, Plant and Equipment:
Natural gas transmission and other plant	8,184.7	8,165.3
Construction work in progress	285.8	258.0
Property, plant and equipment, gross	8,470.5	8,423.3
Less-accumulated depreciation and amortization	1,283.4	1,234.1
Property, plant and equipment, net	7,187.1	7,189.2
Other Assets:
Goodwill	270.8	270.8
Gas stored underground	108.7	109.7
Costs recoverable from customers	14.8	14.9
Other	122.3	124.7
Total other assets	516.6	520.1
Total Assets	7,843.9	7,862.5
Payables:
Trade	43.3	69.8
Affiliates	3.0	2.7
Other	17.3	19.2
Gas Payables:
Transportation	5.8	10.4
Storage	8.6	3.5
Accrued taxes, other	26.1	40.5
Accrued interest	33.5	42.5
Accrued payroll and employee benefits	17.6	25.2
Deferred income	12.6	19.9
Other current liabilities	25.6	22.1
Total current liabilities	193.4	255.8
Long-term debt	3,607.7	3,539.2
Other Liabilities and Deferred Credits:
Pension liability	26.8	26.8
Asset retirement obligation	35.2	33.2
Provision for other asset retirement	58.6	57.4
Payable to affiliate	16.0	16.0
Other	62.1	57.0
Total other liabilities and deferred credits	198.7	190.4
Commitments and Contingencies
Partners' Capital:
Common units - 207.7 million units issued and outstanding as of March 31, 2013 and December 31, 2012	3,164.2	3,190.3
Class B units - 22.9 million units issued and outstanding as of March 31, 2013 and December 31, 2012	678.3	678.3
General partner	75.0	75.8
Accumulated other comprehensive loss	(73.4)	(67.3)
Total partners' capital	3,844.1	3,877.1
Total Liabilities and Partners' Capital	$ 7,843.9	$ 7,862.5