Summary of Significant Accounting Policies (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Movement in Valuation Allowances and Reserves [Roll Forward]
Balance at beginning of period	$ 6.8	$ 5.4	$ 6.1
Additions charged to costs and expenses	0.2	2.3	0.5
Deductions	(1.2)	(0.9)	(1.2)
Balance at end of period	5.8	6.8	5.4
Customer prepayments included in accrued other current liabilities	5.6	7.1
Inventories [Abstract]
Gas in underground storage	61.8	2.2
Gas Imbalances [Abstract]
Gas imbalance receivables	18.8	18.8
Gas imbalance payables	9.7	7.7
Classes And Depreciation [Abstract]
Composite depreciation rate, minimum (in hundredths)	1.60%
Composite depreciation rate, maximum (in hundredths)	12.50%
Allowance for Funds Used During Construction/Capitalized Interest [Abstract]
Allowance for funds used during construction on debt and other capitalized interest	14.5	12.5	32.9
Allowance for funds used during construction on equity	0.2	0.7	22.7
Goodwill [Abstract]
Goodwill	1,436.2	1,233.6	1,149.2
Noncontrolling Interest [Line Items]
Number Of Operating Partnerships	5
Ownership percentage of noncontrolling interest (in hundredths)	1.0101%
Comprehensive Income [Abstract]
Net unrealized gains/(losses) on cash flow hedge derivatives, beginning of period	(307.7)	(418.9)
Change for period	266.8	111.2
Net unrealized gains/(losses) on cash flow hedge derivatives, end of period	(40.9)	(307.7)	(418.9)
Foreign currency translation adjustments, beginning of period	131.9	32.4
Change for period	(44.4)	100.6	252.2
Foreign currency translation adjustments, end of period	87.9	131.9	32.4
Pension and other postretirement liability adjs., beginning of period	43.7	(10.6)	(8.3)
Change for period	(33.5)	(2.3)	(2.5)
Pension and other postretirement liability adjs., end of period	43.7	(10.6)	(8.3)
Total accumulated other comprehensive income/(loss), beginning of period	(186.4)	(394.8)
Change for period	191.5	210.6	(108.2)
Total accumulated other comprehensive income/(loss), end of period	$ 3.3	$ (186.4)	$ (394.8)
Globalplex Partners [Member]
Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest (in hundredths)	50.00%
Ownership percentage of parent (in hundredths)	50.00%
International Marine Terminals Partnership [Member]
Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest (in hundredths)	33.00%
Ownership percentage of parent (in hundredths)	67.00%
Pecos Carbon Dioxide Company [Member]
Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest (in hundredths)	31.00%
Ownership percentage of parent (in hundredths)	69.00%
Guilford County Terminal Company, LLC [Member]
Noncontrolling Interest [Line Items]
Ownership percentage of noncontrolling interest (in hundredths)	35.00%
Ownership percentage of parent (in hundredths)	65.00%

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The high end of the range of composite depreciation rates that are applied to functional groups of property having similar economic characteristics.

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The low end of the range of composite depreciation rates that are applied to functional groups of property having similar economic characteristics.

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The carrying amount of obligations incurred and payable by the Company for gas imbalances. Gas imbalances represent the difference between customer nominations and actual gas receipts from, and gas deliveries to, the Company's interconnecting pipelines and shippers under various operational balancing and shipper imbalance agreements. Natural gas imbalances are either settled in cash or made up in-kind subject to the pipelines' various tariff provisions.

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The carrying amount of receivables due to the Company for gas imbalances. Gas imbalances represent the difference between customer nominations and actual gas receipts from, and gas deliveries to, the Company's interconnecting pipelines and shippers under various operational balancing and shipper imbalance agreements. Natural gas imbalances are either settled in cash or made up in-kind subject to the pipelines' various tariff provisions.

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The number of limited partnerships, referred to as operating partnerships, through which the limited partnership conducts its operations.

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The component of the allowance for funds used during construction during the period comprised of interest on borrowed funds used in financing the construction of regulated assets, which may be reflected as a reduction of interest expense AND the amount of other interest that was capitalized during the period.

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Accumulated change, net of tax, in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges. Includes an entity's share of an equity investee's increase (decrease) in deferred hedging gains or losses.

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The total of net (gain) loss, prior service cost (credit), and transition assets (obligations), as well as minimum pension liability if still remaining, included in accumulated other comprehensive income associated with a defined benefit pension or other postretirement plan(s) because they have yet to be recognized as components of net periodic benefit cost.

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Accumulated adjustment, net of tax, that results from the process of translating subsidiary financial statements and foreign equity investments into the reporting currency from the functional currency of the reporting entity, net of reclassification of realized foreign currency translation gains (losses).

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Accumulated change in equity from transactions and other events and circumstances from non-owner sources, net of tax effect, at fiscal year-end. Excludes Net Income (Loss), and accumulated changes in equity from transactions resulting from investments by owners and distributions to owners. Includes foreign currency translation items, certain pension adjustments, and unrealized gains and losses on certain investments in debt and equity securities as well as changes in the fair value of derivatives related to the effective portion of a designated cash flow hedge.

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The current portion, due within one year or the normal operating cycle, if longer, of prepayments received from customers for goods or services to be provided in the future.

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Carrying amount as of the balance sheet date of natural gas in storage, which is a mixture of gases (liquefied or otherwise), used for fuel and manufacturing purposes, which is ready for sale.

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Carrying amount as of the balance sheet date, which is the cumulative amount paid, adjusted for any amortization recognized prior to adoption of FAS 142 and for any impairment charges, in excess of the fair value of net assets acquired in one or more business combination transactions.

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The equity interest of noncontrolling shareholders, partners or other equity holders in consolidated entity.

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The consolidating entity's interest in net assets of the subsidiary, expressed as a percentage.

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Net changes to accumulated comprehensive income during the period related to benefit plans, after tax.

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Net of tax effect change in accumulated gains and losses from derivative instruments designated and qualifying as the effective portion of cash flow hedges after taxes. A cash flow hedge is a hedge of the exposure to variability in the cash flows of a recognized asset or liability or a forecasted transaction that is attributable to a particular risk. The change includes an entity's share of an equity investee's increase (decrease) in deferred hedging gains or losses.

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Adjustment that results from the process of translating subsidiary financial statements and foreign equity investments into functional currency of the reporting entity, net of tax.

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This element represents Other Comprehensive Income (Loss), Net of Tax, for the period. Includes deferred gains (losses) on qualifying hedges, unrealized holding gains (losses) on available-for-sale securities, minimum pension liability, and cumulative translation adjustment.

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The component of the allowance for funds used during construction during the period based on an assumed rate of return on equity funds used in financing the construction of regulated assets.

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Total of allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs

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Total of the deductions in a given period to allowances and reserves, the valuation and qualifying accounts that are either netted against the cost of an asset (in order to value it at its carrying value) or that reflect a liability established to represent expected future costs, representing receivables written off as uncollectible and portions of the reserves utilized, respectively.

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