Boardwalk Pipeline Partners (BWP) 10-K 20 Feb 15 2014 FY Annual report Financial data

Document_And_Entity_Informatio

Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2014	Feb. 20, 2015	Jun. 30, 2014
Entity Information [Line Items]
Entity Registrant Name	Boardwalk Pipeline Partners, LP
Entity Central Index Key	1336047
Current Fiscal Year End Date	-19
Entity Filer Category	Large Accelerated Filer
Document Type	10-K
Document Period End Date	31-Dec-14
Document Fiscal Year Focus	2014
Document Fiscal Period Focus	FY
Amendment Flag	FALSE
Entity Common Stock, Shares Outstanding		243,223,801
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$2,176,296,858

CONSOLIDATED_BALANCE_SHEETS

CONSOLIDATED BALANCE SHEETS (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Current Assets:
Cash and cash equivalents	$6.60	$28.50
Receivables:
Trade, net	102.6	103.5
Affiliates	0	1.1
Other	8.3	15.7
Gas transportation receivables	9.1	7.8
Gas and liquids stored underground	4.1	0.7
Prepayments	14.5	12.9
Other current assets	4.4	6.9
Total current assets	149.6	177.1
Property, Plant and Equipment:
Natural gas transmission and other plant	9,250.10	8,548.80
Construction work in progress	105.5	174.5
Property, plant and equipment, gross	9,355.60	8,723.30
Less—accumulated depreciation and amortization	1,766.40	1,489.20
Property, plant and equipment, net	7,589.20	7,234.10
Other Assets:
Goodwill	237.4	215.5
Gas stored underground	86.4	79.7
Investment in unconsolidated affiliates	0	78.6
Other	144.2	129.5
Total other assets	468	503.3
Total Assets	8,206.80	7,914.50
Payables:
Trade	51.7	65.1
Affiliates	1.5	1.2
Other	10.4	5.7
Gas payables	8.5	9
Accrued taxes, other	47.1	46.1
Accrued interest	47.4	45.4
Accrued payroll and employee benefits	26.3	26.4
Deferred income	1.9	9.3
Other current liabilities	25.4	27.8
Total current liabilities	220.2	236
Long–term debt and capital lease obligation	3,689.70	3,424.40
Other Liabilities and Deferred Credits:
Pension liability	19.2	17.1
Asset retirement obligation	39.9	39.3
Provision for other asset retirement	60.5	57.6
Payable to affiliate	16	16
Other	59	60.7
Total other liabilities and deferred credits	194.6	190.7
Commitments and Contingencies
Equity:
Common units – 243.3 million units issued and outstanding as of December 31, 2014 and 2013	4,095.10	3,963.40
General partner	80	77.3
Accumulated other comprehensive loss	-72.8	-63.8
Total partners’ capital	4,102.30	3,976.90
Noncontrolling interest	0	86.5
Total Equity	4,102.30	4,063.40
Total Liabilities and Equity	$8,206.80	$7,914.50

CONSOLIDATED_BALANCE_SHEETS_Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Partners' Capital:
Common Units Issued (in shares)	243.3	243.3
Common Units Outstanding (in shares)	243.3	243.3

CONSOLIDATED_STATEMENTS_OF_INC

CONSOLIDATED STATEMENTS OF INCOME (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Revenues:
Transportation	$1,065.10	$1,028	$1,058.30
Parking and lending	23.3	23.9	28
Storage	89.5	110.9	84.7
Other	55.9	42.8	14
Total operating revenues	1,233.80	1,205.60	1,185
Operating Costs and Expenses:
Fuel and transportation	120.7	93.4	79.4
Operation and maintenance	198.8	186.5	167.2
Administrative and general	125	117.4	115.3
Depreciation and amortization	288.7	271.6	252.3
Asset impairment	10.1	4.1	9.1
Goodwill impairment	0	51.5	0
Net gain on sale of operating assets	-1.1	-29.5	-3.3
Taxes other than income taxes	93.5	96.1	91.2
Total operating costs and expenses	835.7	791.1	711.2
Operating income	398.1	414.5	473.8
Other Deductions (Income):
Interest expense	165.5	163.4	161.5
Interest expense – affiliates	0	0	6.9
Interest income	-0.6	-0.5	-0.7
Equity losses in unconsolidated affiliates	86.5	1.2	0
Miscellaneous other income	-0.5	-0.3	-0.4
Total other deductions	250.9	163.8	167.3
Income before income taxes	147.2	250.7	306.5
Income taxes	0.4	0.5	0.5
Net Income	146.8	250.2	306
Net loss attributable to noncontrolling interests	-86.8	-3.5	0
Net income attributable to controlling interests	$233.60	$253.70	$306

CONSOLIDATED_STATEMENTS_OF_INC1

CONSOLIDATED STATEMENTS OF INCOME Net Income Per Unit (USD $)	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Common Units
Basic net income per unit:
Basic net income per unit	$0.94	$1	$1.37
Weighted-average number of units outstanding - basic
Weighted-average number of units outstanding - basic	243.3	220.5	191.9
Diluted net income per unit:
Diluted net income per unit	$0.94	$0.96	$1.37
Weighted-average number of units outstanding - diluted
Weighted-average number of units outstanding - diluted	243.3	226.8	191.9
Distribution Made to Limited Partner, Distributions Paid, Per Unit	$0.40	$2.13	$2.13
Class B Units
Basic net income per unit:
Basic net income per unit	$0	$0.05	$0.36
Weighted-average number of units outstanding - basic
Weighted-average number of units outstanding - basic	0	17.6	22.9
Diluted net income per unit:
Diluted net income per unit	$0	$0.48	$0.36
Weighted-average number of units outstanding - diluted
Weighted-average number of units outstanding - diluted	0	11.3	22.9
Distribution Made to Limited Partner, Distributions Paid, Per Unit	$0	$0.90	$1.20

CONSOLIDATED_STATEMENTS_OF_COM

CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Statement of Comprehensive Income [Abstract]
Net Income	$36.90	$28.40	$55.90	$25.60	$16.70	$61.70	$70.40	$101.40	$146.80	$250.20	$306
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									-0.7	1.6	-7.1
Reclassification adjustment transferred to Net income from cash flow hedges									2.6	1.2	2
Pension and other postretirement benefit costs									-10.9	0.7	-12.8
Total Comprehensive Income									137.8	253.7	288.1
Comprehensive loss attributable to noncontrolling interests									-86.8	-3.5	0
Comprehensive income attributable to controlling interests									$224.60	$257.20	$288.10

CONSOLIDATED_STATEMENTS_OF_CAS

CONSOLIDATED STATEMENTS OF CASH FLOWS (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Activities:
Net Income	$146.80	$250.20	$306
Adjustments to reconcile net income to cash provided by operations:
Depreciation and amortization	288.7	271.6	252.3
Amortization of deferred costs	5.7	5.5	6.4
Asset impairment	10.1	4.1	9.1
Goodwill impairment	0	51.5	0
Net gain on sale of operating assets	-1.1	-29.5	-3.3
Equity losses in unconsolidated affiliates	86.5	1.2	0
Changes in operating assets and liabilities:
Trade and other receivables	8.3	-10	5.4
Other receivables, affiliates	1	0.5	0.1
Gas receivables and storage assets	-11.5	18	-10.4
Costs recoverable from customers	0.5	2.6	6.5
Other assets	5.8	-10.7	-1.7
Trade and other payables	-7.3	-16.8	8.3
Other payables, affiliates	0.2	0.7	-3.1
Gas payables	-8.8	0.5	13.5
Accrued liabilities	3.9	8.6	-1.5
Other liabilities	-15.2	-13.7	-12.1
Net cash provided by operating activities	513.6	534.3	575.5
INVESTING ACTIVITIES:
Capital expenditures	-404.4	-294.8	-226.9
Proceeds from sale of operating assets	2.9	60.7	5.9
Proceeds from insurance and other recoveries	6.3	1.4	10.4
Advances to affiliates	0.1	0	0
Investment in unconsolidated affiliates	-20.5	-76.7	0
Distribution from unconsolidated affiliates	11.1	0	0
Acquisition of businesses, net of cash acquired	-294.7	0	-620.2
Net cash used in investing activities	-699.2	-309.4	-830.8
FINANCING ACTIVITIES:
Proceeds from long-term debt	342.9	0	818
Repayment of borrowings from long-term debt	0	0	-525
Proceeds from borrowings on revolving credit agreement	665	1,128	2,135
Repayment of borrowings on revolving credit agreement, including financing costs	-720	-1,255	-2,295.30
Repayment of borrowings from term loan	-25	0	0
Principal payment of capital lease obligation	-0.4	-0.2	0
Contribution received related to predecessor equity	0	0	269.2
Repayment of contribution received related to predecessor equity	0	0	-554
Advances from affiliate	0.1	-2.8	2.6
Distributions paid	-99.2	-533.9	-478.9
Capital contributions from noncontrolling interests	8.2	87.1	0
Proceeds from sale of common units	0	368.7	847.7
Capital contribution from general partner	0	7.8	18
Distributions paid to noncontrolling interests	-7.9	0	0
Net cash provided (used in) by financing activities	163.7	-200.3	237.3
(Decrease) increase in cash and cash equivalents	-21.9	24.6	-18
Cash and cash equivalents at beginning of period	28.5	3.9	21.9
Cash and cash equivalents at end of period	$6.60	$28.50	$3.90

CONSOLIDATED_STATEMENTS_OF_CHA

CONSOLIDATED STATEMENTS OF CHANGES IN EQUITY (USD $)	Total	General Partner	Limited Partner	Limited Partner	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interests	Predecessor Equity
In Millions, unless otherwise specified			Common Units	Class B Units
Beginning Balance at Dec. 31, 2011	$3,487	$62	$2,514.10	$678.70	($49.40)	$0	$281.60
Add (deduct):
Net income (loss)	306	35.7	245	27.5	0	0	-2.2
Distributions paid	-478.9	-39.7	-411.8	-27.4	0	0	0
Sale of common units, net of related transaction costs	847.7	0	847.7	0	0	0	0
Capital contribution from general partner	18	18	0	0	0	0	0
Contribution received related to predecessor equity	269.2	0	0	0	0	0	269.2
Predecessor equity carrying amount of acquired entities	-548.6	0	0	0	0	0	-548.6
Excess purchase price over net acquired assets	-5.4	-0.2	-4.7	-0.5	0	0	0
Other comprehensive income (loss), net of tax	-17.9	0	0	0	-17.9	0	0
Ending Balance at Dec. 31, 2012	3,877.10	75.8	3,190.30	678.3	-67.3	0	0
Add (deduct):
Net income (loss)	250.2	39	194.5	20.2	0	-3.5	0
Distributions paid	-533.9	-45.3	-468	-20.6	0	0	0
Sale of common units, net of related transaction costs	368.7	0	368.7	0	0	0	0
Capital contribution from general partner	7.8	7.8	0	0	0	0	0
Conversion of class B units to common units	0	0	677.9	-677.9	0	0	0
Contribution received related to predecessor equity	0
Capital contributions from noncontrolling interests	90	0	0	0	0	90	0
Other comprehensive income (loss), net of tax	3.5	0	0	0	3.5	0	0
Ending Balance at Dec. 31, 2013	4,063.40	77.3	3,963.40	0	-63.8	86.5	0
Add (deduct):
Net income (loss)	146.8	4.7	228.9	0	0	-86.8	0
Distributions paid	-99.2	-2	-97.2	0	0	0	0
Contribution received related to predecessor equity	0
Capital contributions from noncontrolling interests	8.2	0	0	0	0	8.2	0
Distributions paid to noncontrolling interests	-7.9	0	0	0	0	-7.9	0
Other comprehensive income (loss), net of tax	-9	0	0	0	-9	0	0
Ending Balance at Dec. 31, 2014	$4,102.30	$80	$4,095.10	$0	($72.80)	$0	$0

Corporate_Structure

Corporate Structure	12 Months Ended
	Dec. 31, 2014
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Corporate Structure	Note 1:  Corporate Structure
	Boardwalk Pipeline Partners, LP (the Partnership) is a Delaware limited partnership formed in 2005 to own and operate the business conducted by its primary subsidiary Boardwalk Pipelines, LP (Boardwalk Pipelines) and its operating subsidiaries, Gulf South Pipeline Company, LP (Gulf South), Texas Gas Transmission, LLC (Texas Gas), Gulf Crossing Pipeline Company LLC (Gulf Crossing), Boardwalk Louisiana Midstream, LLC (Louisiana Midstream), Boardwalk Petrochemical Pipeline, LLC (Boardwalk Petrochemical) and Boardwalk Field Services, LLC (Field Services) (together, the operating subsidiaries), and consists of integrated natural gas and natural gas liquids (NGLs) pipeline and storage systems and natural gas gathering and processing. Petal Gas Storage, LLC (Petal) was merged into Gulf South effective January 1, 2015. All of the Partnership’s operations are conducted by its operating subsidiaries.
	As of February 20, 2015, Boardwalk Pipelines Holding Corp. (BPHC), a wholly-owned subsidiary of Loews Corporation (Loews), owned 125.6 million of the Partnership’s common units, and, through Boardwalk GP, LP (Boardwalk GP), an indirect wholly-owned subsidiary of BPHC, holds the 2% general partner interest and all of the incentive distribution rights (IDRs). As of February 20, 2015, the common units and general partner interest owned by BPHC represent approximately 53% of the Partnership’s equity interests, excluding the IDRs. The Partnership's Class B limited partner interests converted to common units on a one-for-one basis on October 9, 2013. The Partnership’s common units are traded under the symbol “BWP” on the New York Stock Exchange.
	Basis of Presentation
	The accompanying consolidated financial statements of the Partnership were prepared in accordance with accounting principles generally accepted in the United States of America (GAAP).

Accounting_Policies

Accounting Policies	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Accounting Policies	Note 2:  Accounting Policies
	Principles of Consolidation
	The consolidated financial statements include the Partnership’s accounts and those of its wholly-owned subsidiaries after elimination of intercompany transactions. The Partnership also consolidates variable interest entities (VIEs) in which the Partnership is the primary beneficiary. Third party or affiliate ownership interests in the Partnership's subsidiaries and consolidated VIEs are presented as noncontrolling interests.
	The Partnership applies the equity method of accounting for investments in unconsolidated affiliates in which it owns 20 percent to 50 percent of the voting interests or otherwise exercises significant influence, but not control, over operating and financial policies of the investee. Under this method, the carrying amounts of the Partnership's equity investments are increased by a proportionate share of the investee's net income and contributions made, and decreased by a proportionate share of the investee's net losses and distributions received.
	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and disclosure of contingent assets and liabilities and the fair values of certain items. The Partnership bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, which form the basis for making judgments about the carrying amounts of assets and liabilities that are not readily apparent from other sources. Actual results could differ from such estimates.
	Segment Information
	The Partnership operates in one reportable segment - the operation of interstate natural gas and NGLs pipeline systems including integrated storage facilities. This segment consists of interstate natural gas pipeline systems which originate in the Gulf Coast region, Oklahoma and Arkansas, and extend north and east through the Midwestern states of Tennessee, Kentucky, Illinois, Indiana and Ohio and NGLs pipelines and storage facilities in Louisiana and Texas.
	Regulatory Accounting
	Most of the Partnership's natural gas pipeline subsidiaries are regulated by the Federal Energy Regulatory Commission (FERC). When certain criteria are met, GAAP requires that certain rate-regulated entities account for and report assets and liabilities consistent with the economic effect of the manner in which independent third-party regulators establish rates (regulatory accounting). This basis of accounting is applicable to operations of the Partnership’s Texas Gas subsidiary which records certain costs and benefits as regulatory assets and liabilities in order to provide for recovery from or refund to customers in future periods, but is not applicable to operations associated with the Fayetteville and Greenville Laterals due to rates charged under negotiated rate agreements and a portion of the storage capacity due to the regulatory treatment associated with the rates charged for that capacity. Regulatory accounting is not applicable to the Partnership’s other FERC-regulated entities.
	The Partnership monitors the regulatory and competitive environment in which it operates to determine that its regulatory assets continue to be probable of recovery. If the Partnership were to determine that all or a portion of its regulatory assets no longer met the criteria for recognition as regulatory assets, that portion which was not recoverable would be written off, net of any regulatory liabilities.
	Note 10 contains more information regarding the Partnership’s regulatory assets and liabilities.
	Fair Value Measurements
	Fair value refers to an exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction in the principal market in which the reporting entity transacts based on the assumptions market participants would use when pricing the asset or liability assuming its highest and best use. A fair value hierarchy has been established that prioritizes the information used to develop those assumptions giving priority, from highest to lowest, to quoted prices in active markets for identical assets and liabilities (Level 1); observable inputs not included in Level 1, for example, quoted prices for similar assets and liabilities (Level 2); and unobservable data (Level 3), for example, a reporting entity’s own internal data based on the best information available in the circumstances. The Partnership uses fair value measurements to record derivatives, asset retirement obligations and impairments. Fair value measurements are also used to perform goodwill impairment testing and report fair values for certain items contained in this Report. The Partnership considers any transfers between levels within the fair value hierarchy to have occurred at the beginning of a quarterly reporting period.  The Partnership did not recognize any transfers between Level 1 and Level 2 of the fair value hierarchy and did not change its valuation techniques or inputs during the year ended December 31, 2014.
	Notes 6 and 12 contain more information regarding fair value measurements.
	Cash and Cash Equivalents
	Cash equivalents are highly liquid investments with an original maturity of three months or less and are stated at cost plus accrued interest, which approximates fair value. The Partnership had no restricted cash at December 31, 2014 and 2013.
	Cash Management
	The operating subsidiaries participate in an intercompany cash management program with those that are FERC-regulated participating to the extent they are permitted under FERC regulations. Under the cash management program, depending on whether a participating subsidiary has short-term cash surpluses or cash requirements, Boardwalk Pipelines either provides cash to them or they provide cash to Boardwalk Pipelines. The transactions are represented by demand notes and are stated at historical carrying amounts. Interest income and expense is recognized on an accrual basis when collection is reasonably assured. The interest rate on intercompany demand notes is London Interbank Offered Rate (LIBOR) plus one percent and is adjusted every three months.
	Trade and Other Receivables
	Trade and other receivables are stated at their historical carrying amount, net of allowances for doubtful accounts. The Partnership establishes an allowance for doubtful accounts on a case-by-case basis when it believes the required payment of specific amounts owed is unlikely to occur. Uncollectible receivables are written off when a settlement is reached for an amount that is less than the outstanding historical balance or a receivable amount is deemed otherwise unrealizable.
	Gas Stored Underground and Gas Receivables and Payables
	Certain of the Partnership's operating subsidiaries have underground gas in storage which is utilized for system management and operational balancing, as well as for services including firm and interruptible storage associated with certain no-notice and parking and lending (PAL) services. Gas stored underground includes the historical cost of natural gas volumes owned by the operating subsidiaries, at times reduced by certain operational encroachments upon that gas. Current gas stored underground represents net retained fuel remaining after providing transportation and storage services which is available for resale and is valued at the lower of weighted-average cost or market.
	The operating subsidiaries provide storage services whereby they store natural gas or NGLs on behalf of customers and also periodically hold customer gas under PAL services. Since the customers retain title to the gas held by the Partnership in providing these services, the Partnership does not record the related gas on its balance sheet. Certain of the Partnership's operating subsidiaries also periodically lend gas and NGLs to customers.
	In the course of providing transportation and storage services to customers, the operating subsidiaries may receive different quantities of gas from shippers and operators than the quantities delivered on behalf of those shippers and operators. This results in transportation and exchange gas receivables and payables, commonly known as imbalances, which are settled in cash or the receipt or delivery of gas in the future. Settlement of imbalances requires agreement between the pipelines and shippers or operators as to allocations of volumes to specific transportation contracts and timing of delivery of gas based on operational conditions.  The receivables and payables are valued at market price for operations where regulatory accounting is not applicable and are valued at the historical value of gas in storage for operations where regulatory accounting is applicable.
	Materials and Supplies
	Materials and supplies are carried at average cost and are included in Other Assets on the Consolidated Balance Sheets. The Partnership expects its materials and supplies to be used for capital projects related to its property, plant and equipment and for future growth projects. At December 31, 2014 and 2013, the Partnership held approximately $15.3 million and $12.8 million of materials and supplies which were reflected in Other Assets on the Consolidated Balance Sheets.
	Property, Plant and Equipment (PPE) and Repair and Maintenance Costs
	PPE is recorded at its original cost of construction or fair value of assets purchased. Construction costs and expenditures for major renewals and improvements which extend the lives of the respective assets are capitalized. Construction work in progress is included in the financial statements as a component of PPE. All repair and maintenance costs are expensed as incurred.
	Depreciation of PPE related to operations for which regulatory accounting does not apply is provided for using the straight-line method of depreciation over the estimated useful lives of the assets, which range from 3 to 35 years. The ordinary sale or retirement of PPE for these assets could result in a gain or loss. Depreciation of PPE related to operations for which regulatory accounting is applicable is provided for primarily on the straight-line method at FERC-prescribed rates over estimated useful lives of 5 to 62 years. Reflecting the application of composite depreciation, gains and losses from the ordinary sale or retirement of PPE for these assets are not recognized in earnings and generally do not impact PPE, net.
	Note 7 contains more information regarding the Partnership’s PPE.
	Goodwill and Intangible Assets
	Goodwill represents the excess of the cost of an acquisition over the fair value of the net identifiable assets acquired and liabilities assumed. Goodwill is tested for impairment at the reporting unit level at least annually, as of November 30, or more frequently when events occur and circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Accounting requirements provide that a reporting entity may perform an optional qualitative assessment on an annual basis to determine whether events occurred or circumstances changed that would more likely than not reduce the fair value of a reporting unit below its carrying amount. If an initial qualitative assessment identifies that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, or the optional qualitative assessment is not performed, a quantitative analysis is performed under a two-step impairment test to measure whether the fair value of the reporting unit is less than its carrying amount. If based upon a quantitative analysis the fair value of the reporting unit is less than its carrying amount, including goodwill, the Partnership performs an analysis of the fair value of all the assets and liabilities of the reporting unit. If the implied fair value of the reporting unit's goodwill is determined to be less than its carrying amount, an impairment loss is recognized for the difference.
	Intangible assets are those assets which provide future economic benefit but have no physical substance. The Partnership recorded intangible assets for customer relationships obtained through its acquisitions. The customer relationships, which are included in Other Assets on the Consolidated Balance Sheets, have a finite life and are being amortized in a systematic and rational manner over their estimated useful lives.
	Note 8 contains additional information regarding the Partnership's goodwill and intangible assets.
	Impairment of Long-lived Assets (including Tangible and Definite-lived Intangible Assets)
	The Partnership evaluates its long-lived and intangible assets for impairment when, in management’s judgment, events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. When such a determination has been made, management’s estimate of undiscounted future cash flows attributable to the remaining economic useful life of the asset is compared to the carrying amount of the asset to determine whether an impairment has occurred. If an impairment of the carrying amount has occurred, the amount of impairment recognized in the financial statements is determined by estimating the fair value of the assets and recording a loss to the extent that the carrying amount exceeds the estimated fair value.
	Capitalized Interest and Allowance for Funds Used During Construction (AFUDC)
	The Partnership records capitalized interest, which represents the cost of borrowed funds used to finance construction activities for operations where regulatory accounting is not applicable. The Partnership records AFUDC, which represents the cost of funds, including equity funds, applicable to regulated natural gas transmission plant under construction as permitted by FERC regulatory practices, in connection with the Partnership’s operations where regulatory accounting is applicable. Capitalized interest and the allowance for borrowed funds used during construction are recognized as a reduction to Interest expense and the allowance for equity funds used during construction is included in Miscellaneous other income, net within the Consolidated Statements of Income. The following table summarizes capitalized interest and the allowance for borrowed funds and allowance for equity funds used during construction (in millions):
		For the Year Ended
		December 31,
		2014		2013		2012
	Capitalized interest and allowance for borrowed funds used during construction	$	6.8	$	6.4	$	4.7
	Allowance for equity funds used during construction	0.5		0.2		0.4
	Income Taxes
	The Partnership is not a taxable entity for federal income tax purposes.  As such, it does not directly pay federal income tax. The Partnership’s taxable income or loss, which may vary substantially from the net income or loss reported in the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. The aggregate difference in the basis of the Partnership’s net assets for financial and income tax purposes cannot be readily determined as the Partnership does not have access to the information about each partner’s tax attributes related to the Partnership. The subsidiaries of the Partnership directly incur some income-based state taxes which are presented in Income taxes on the Consolidated Statements of Income.
	Note 14 contains more information regarding the Partnership’s income taxes.
	Revenue Recognition
	The maximum rates that may be charged by the majority of the Partnership's operating subsidiaries for their services are established through FERC’s cost-based rate-making process; however, rates charged by those operating subsidiaries may be less than those allowed by FERC. Revenues from transportation and storage services are recognized in the period the service is provided based on contractual terms and the related volumes transported or stored. In connection with some PAL and interruptible storage service agreements, cash is received at inception of the service period resulting in the recording of deferred revenues which are recognized in revenues over the period the services are provided. At December 31, 2014 and 2013, the Partnership had deferred revenues of $1.0 million and $7.9 million related to PAL and interruptible storage services and $6.2 million and $4.6 million related to a firm transportation agreement that was paid in advance. At December 31, 2014, the Partnership had deferred revenues of $2.5 million related to a brine supply contract for which certain future minimum volumes will need to be supplied by the Partnership. The deferred revenues related to PAL and interruptible storage services will be recognized through 2017 and the deferred revenues related to the firm transportation agreement will be recognized through 2018.
	Retained fuel is recognized in revenues at market prices in the month of retention for operations where regulatory accounting is not applicable. The related fuel consumed in providing transportation services is recorded in Fuel and transportation expenses at market prices in the month consumed. In some cases, customers may elect to pay cash for the cost of fuel used in providing transportation services instead of having fuel retained in-kind. Retained fuel included in Transportation on the Consolidated Statements of Income for the years ended December 31, 2014, 2013 and 2012 was $90.3 million, $76.9 million and $71.8 million.
	The Partnership has contractual retainage provisions in some of its ethylene storage contracts that provide for the Partnership to retain ownership of 0.5% of customer inventory volumes injected into storage wells. The Partnership may sell the retainage volumes if commercially marketable volumes are on hand. The Partnership recognizes revenue for ethylene retainage volumes upon the physical sale of such volumes.
	Under FERC regulations, certain revenues that the operating subsidiaries collect may be subject to possible refunds to customers. Accordingly, during a rate case, estimated refund liabilities are recorded considering regulatory proceedings, advice of counsel and estimated risk-adjusted total exposure, as well as other factors. At December 31, 2014 and 2013, there were no liabilities for any open rate case recorded on the Consolidated Balance Sheets.
	Asset Retirement Obligations
	The accounting requirements for existing legal obligations associated with the future retirement of long-lived assets require entities to record the fair value of a liability for an asset retirement obligation in the period during which the liability is incurred. The liability is initially recognized at fair value and is increased with the passage of time as accretion expense is recorded, until the liability is ultimately settled. The accretion expense is included within Operation and maintenance costs within the Consolidated Statements of Income. An amount corresponding to the amount of the initial liability is capitalized as part of the carrying amount of the related long-lived asset and depreciated over the useful life of that asset.
	Note 9 contains more information regarding the Partnership’s asset retirement obligations.
	Environmental Liabilities
	The Partnership records environmental liabilities based on management’s estimate of the undiscounted future obligation for probable costs associated with environmental assessment and remediation of operating sites. These estimates are based on evaluations and discussions with counsel and operating personnel and the current facts and circumstances related to these environmental matters.
	Note 5 contains more information regarding the Partnership’s environmental liabilities.
	Defined Benefit Plans
	The Partnership maintains certain postretirement benefit plans for certain employees. The Partnership funds these plans through periodic contributions which are invested until the benefits are paid out to the participants. The net benefit cost of the plan is recorded in the Consolidated Statements of Income. The Partnership records an asset or liability based on the overfunded or underfunded status of the plan. Any deferred amounts related to unrecognized gains and losses or changes in actuarial assumptions are recorded as either a regulatory asset or liability or recorded as a component of accumulated other comprehensive income (AOCI) until those gains or losses are recognized in the Consolidated Statements of Income.
	Note 12 contains more information regarding the Partnership’s pension and postretirement benefit obligations.
	Unit-Based and Other Long-Term Compensation
	The Partnership provides awards of phantom common units (Phantom Common Units) to certain employees under its Long-Term Incentive Plan (LTIP). The Partnership also provides to certain employees awards of unit appreciation rights (UARs) and long-term cash bonuses (Long-Term Cash Bonuses) under the Boardwalk Pipeline Partners Unit Appreciation Rights and Cash Bonus Plan. In 2014, the Partnership entered into retention payment agreements with certain key employees.
	The Partnership measures the cost of an award issued in exchange for employee services based on the grant-date fair value of the award, or the stated amount in the case of the Long-Term Cash Bonuses and amounts under retention payment agreements. All outstanding awards are either required or expected to be settled in cash and are classified as a liability until settlement. The unit-based compensation awards are remeasured each reporting period until the final amount of awards is determined. The related compensation expense, less applicable estimates of forfeitures, is recognized over the period that employees are required to provide services in exchange for the awards, usually the vesting period.
Note 12 contains additional information regarding the Partnership’s unit-based and other long-term compensation.
Partner Capital Accounts
For purposes of maintaining capital accounts, items of income and loss of the Partnership are allocated among the partners each year, or portion thereof, in accordance with the partnership agreement. Generally, net income for each period is allocated among the partners based on their respective ownership interests after deducting any priority allocations in the form of cash distributions paid to the general partner as the holder of IDRs.
Derivative Financial Instruments
The Partnership uses futures, swaps, and option contracts (collectively, derivatives) to hedge exposure to various risks, including natural gas commodity and interest rate risk. The effective portion of the related unrealized gains and losses resulting from changes in fair values of the derivatives contracts designated as cash flow hedges are deferred as a component of AOCI. The deferred gains and losses are recognized in earnings when the hedged anticipated transactions affect earnings. Changes in fair value of derivatives that are not designated as cash flow hedges are recognized in earnings in the periods that those changes in fair value occur.
The changes in fair values of the derivatives designated as cash flow hedges are expected to, and do, have a high correlation to changes in value of the anticipated transactions. Each reporting period the Partnership measures the effectiveness of the cash flow hedge contracts. To the extent the changes in the fair values of the hedge contracts do not effectively offset the changes in the estimated cash flows of the anticipated transactions, the ineffective portion of the hedge contracts is currently recognized in earnings. If it becomes probable that the anticipated transactions will not occur, hedge accounting would be terminated and changes in the fair values of the associated derivative financial instruments would be recognized currently in earnings. The Partnership discontinued an immaterial amount of cash flow hedges in 2014 and did not discontinue any cash flow hedges during 2013.
The effective component of gains and losses resulting from changes in fair values of the derivatives designated as cash flow hedges are deferred as a component of AOCI. The deferred gains and losses associated with the anticipated operational sale of gas reported as current Gas stored underground are recognized in operating revenues when the anticipated transactions affect earnings. In situations where continued reporting of a loss in AOCI would result in recognition of a future loss on the combination of the derivative and the hedged transaction, the loss is required to be immediately recognized in earnings for the amount that is not expected to be recovered. No such losses were recognized in the years ended December 31, 2014, 2013, and 2012.
Note 6 contains more information regarding the Partnership’s derivative financial instruments.

Investments

Investments	12 Months Ended
	Dec. 31, 2014
Investments [Abstract]
Consolidation, Variable Interest Entity, Policy [Policy Text Block]	Note 3: Investments
	Bluegrass Pipeline, Moss Lake Fractionation and Moss Lake LPG Terminal Projects
	In 2013, the Partnership executed an agreement with the Williams Companies, Inc (Williams) to develop the Bluegrass Pipeline, Moss Lake Fractionation and Moss Lake LPG Terminal Projects - projects that would transport NGLs from the Marcellus and Utica shale production areas to the Lake Charles, Louisiana area, and the construction of related fractionation, storage and liquefied petroleum gas terminal export facilities (collectively, the Bluegrass Project). In 2014, due to cost escalations, construction delays and lack of customer commitments, among other things, the Bluegrass Project entities expensed the previously capitalized project costs related to the development process resulting in a $92.9 million charge, which was reflected in Equity losses in unconsolidated affiliates and Asset impairment on the income statement. Net of noncontrolling interests of $82.9 million associated with the Bluegrass investment, these expenses reduced the Partnership’s Net income attributable to controlling interests by $10.0 million. In the fourth quarter 2014, the Partnership and Williams dissolved the Bluegrass Project entities.
	At December 31, 2014, the Partnership had no remaining investment balance related to the Bluegrass Project entities. At December 31, 2013, the Partnership had included $15.0 million of cash, $78.6 million of investments in unconsolidated affiliates, $6.8 million of construction work in progress and $4.9 million of trade and other payables in its Consolidated Balance Sheet related to amounts recorded by Boardwalk Bluegrass Pipeline, LLC and Boardwalk Moss Lake LLC, which were consolidated by the Partnership in accordance with accounting requirements for VIEs.

Acquisition_of_Boardwalk_Petro

Acquisition of Boardwalk Petrochemical	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Business Combination Disclosure [Text Block]	Note 4:  Acquisition of Boardwalk Petrochemical
	On October 8, 2014, the Partnership completed the acquisition of Boardwalk Petrochemical, formerly known as Chevron Petrochemical Pipeline, LLC, which owns and operates the Evangeline ethylene pipeline system (Evangeline), from Chevron Pipe Line Company for $294.7 million in cash, subject to customary adjustments. This acquisition was made as part of the Partnership's long-term growth and diversification strategy and to complement the Partnership's existing NGLs and ethylene midstream assets. The purchase price was funded through borrowings under the Partnership's revolving credit facility.
	The acquisition of Evangeline was accounted for as a business combination using the acquisition method of accounting. The estimated fair values of the assets acquired and liabilities assumed related to the acquisition were as follows (in millions):
		Evangeline Acquisition Date
		Fair Value (3)
	Plant, property and equipment	$	253.3
	Customer-based intangibles (1)	20
	Goodwill (2)	21.9
	Total assets acquired	295.2
	Current liabilities	(0.3		)
	Noncurrent liabilities	(0.2		)
	Total liabilities assumed	(0.5		)
	Net assets acquired	$	294.7
	-1	Customer-based intangibles are estimated to have a weighted-average useful life of 30 years.
	-2	Goodwill represents the excess of the purchase price over the estimated fair value of the assets acquired, net of the fair value of the liabilities assumed in the acquisition.
	-3	The purchase price allocation is preliminary and is subject to change based on the final working capital adjustments which are expected to be settled in the first quarter 2015. For the period from October 8, 2014 to December 31, 2014, Evangeline contributed $0.7 million to the Partnership’s revenues and decreased the Partnership's net income by $1.8 million, excluding acquisition costs. The Partnership incurred $2.6 million of costs related to the acquisition of Boardwalk Petrochemical, which were expensed as incurred and were recorded in Administrative and general expenses. Pro forma data is not provided because the impact of the acquisition on the Partnership’s revenues and net income was not material.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 5: Commitments and Contingencies
	Legal Proceedings and Settlements
	The Partnership's subsidiaries are parties to various legal actions arising in the normal course of business. Management believes the disposition of these outstanding legal actions will not have a material impact on the Partnership's financial condition, results of operations or cash flows.
	Whistler Junction Matter
	The Partnership's Gulf South subsidiary and several other defendants, including Mobile Gas Service Corporation (MGSC), have been named as defendants in ten lawsuits, including one purported class action suit, commenced by multiple plaintiffs in the Circuit Court of Mobile County, Alabama. The plaintiffs seek unspecified damages for personal injury and property damage related to an alleged release of mercaptan at the Whistler Junction facilities in Eight Mile, Alabama. Gulf South delivers natural gas to MGSC, the local distribution company for that region, at Whistler Junction where MGSC odorizes the gas prior to delivery to end user customers by injecting mercaptan into the gas stream, as required by law. The cases are: Parker, et al. v. MGSC, et al. (Case No. CV-12-900711), Crum, et al. v. MGSC, et al. (Case No. CV-12-901057), Austin, et al. v. MGSC, et al. (Case No. CV-12-901133), Moore, et al. v. MGSC, et al. (Case No. CV-12-901471), Davis, et al. v. MGSC, et al. (Case No. CV-12-901490), Joel G. Reed, et al. v. MGSC, et al. (Case No. CV-2013-922265), The Housing Authority of the City of Prichard, Alabama v. MGSC., et al. (Case No. CV-2013-901002), Robert Evans, et al. v. MGSC, et al. (Case No. CV-2013-902627), Devin Nobles, et al. v. MGSC, et al. (Case No. CV-2013-902786) and Richard Eldridge, et al. v. MGSC., et al. (Case No. CV-2014-903209).
	In May 2014, Gulf South and MGSC reached an agreement whereby MGSC fully indemnified Gulf South against all liability related to this matter and the cross-claims between Gulf South and MGSC were settled.
	Southeast Louisiana Flood Protection Litigation
	The Partnership and its subsidiary, Gulf South, along with approximately 100 other energy companies operating in Southern Louisiana, have been named as defendants in a petition for damages and injunctive relief in state district court for Orleans Parish, Louisiana (Case No. 13-6911) by the Board of Commissioners of the Southeast Louisiana Flood Protection Authority - East (Flood Protection Authority). The case was filed in state court, but was removed to the United States District Court for the Eastern District of New Orleans (Court) in August 2013. The lawsuit claims include negligence, strict liability, public nuisance, private nuisance, breach of contract, and breach of the natural servitude of drain against the defendants, alleging that the defendants’ drilling, dredging, pipeline and industrial operations since the 1930s have caused increased storm surge risk, increased flood protection costs and unspecified damages to the Flood Protection Authority. In addition to attorney fees and unspecified monetary damages, the lawsuit seeks abatement and restoration of the coastal lands, including backfilling and revegetating of canals dredged and used by the defendants, and abatement and restoration activities such as wetlands creation, reef creation, land bridge construction, hydrologic restoration, shoreline protection, structural protection, bank stabilization, and ridge restoration. Motions to dismiss have been filed and are pending before the Court and on February 13, 2015, the court dismissed the case with prejudice.
	Environmental and Safety Matters
	The operating subsidiaries are subject to federal, state, and local environmental laws and regulations in connection with the operation and remediation of various operating sites. As of December 31, 2014, and 2013, the Partnership had an accrued liability of approximately $6.1 million and $6.5 million related to assessment and/or remediation costs associated with the historical use of polychlorinated biphenyls, petroleum hydrocarbons and mercury, groundwater protection measures and other costs. The liability represents management’s estimate of the undiscounted future obligations based on evaluations and discussions with counsel and operating personnel and the current facts and circumstances related to these matters. The related expenditures are expected to occur over the next seven years. As of December 31, 2014 and 2013, approximately $1.5 million was recorded in Other current liabilities and approximately $4.6 million and $5.0 million were recorded in Other Liabilities and Deferred Credits.
	Clean Air Act
	The Partnership’s pipelines are subject to the Clean Air Act, as amended, (CAA) and the CAA Amendments of 1990, as amended, (Amendments) which added significant provisions to the CAA. The Amendments require the Environmental Protection Agency (EPA) to promulgate new regulations pertaining to mobile sources, air toxics, areas of ozone non-attainment, greenhouse gases and regulations affecting reciprocating engines subject to Maximum Achievable Control Technology (MACT). The operating subsidiaries presently operate two facilities in areas affected by non-attainment requirements for the current ozone standard (8-hour ozone standard). If the EPA designates additional new non-attainment areas or promulgates new air regulations where the Partnership operates, the cost of additions to PPE is expected to increase. The Partnership has assessed the impact of the CAA on its facilities and does not believe compliance with these regulations will have a material impact on its financial condition, results of operations or cash flows.
	On November 25, 2014, the EPA issued a proposed rulemaking that would lower the 8-hour ozone standard relevant to non-attainment areas. The EPA is proposing to lower the ozone standard to somewhere between 65 parts per billion (ppb) and 70 ppb for both the 8-hour primary and secondary standards that are protective of public health and public welfare. Also, the EPA requested public comments on whether the standard should be set as low as 60 ppb or whether the existing 75 ppb standard should be retained. Under the proposal, the EPA anticipates taking final action by October 1, 2015, designating new non-attainment areas by October 1, 2017, and requiring states to revise implementation plans by October 1, 2020, with compliance dates anticipated between 2021 and 2037 determined by the degree of non-attainment. If the EPA lowers the ozone standard, states could be required to implement new more stringent regulations, which could apply to our and our exploration and production customers’ operations. In particular, compliance with these or other new regulations could, among other things, require installation of new emission controls on some of our equipment, result in longer permitting timelines, and significantly increase our capital expenditures and operating costs, which could adversely impact our business. Since non-attainment area designations will likely be based on 2014-2016 air quality monitoring data and because states will likely pursue various means to achieve the necessary reductions, additional facility impacts cannot be determined at this time. The Partnership will continue to monitor the rulemaking process relative to potentially impacted facilities.
	The Partnership is required to file annual reports with the EPA regarding greenhouse gas (GHG) emissions from its compressor stations, pursuant to final rules issued by the EPA regarding the reporting of greenhouse gas emissions from sources in the United States (U.S.) that annually emit 25,000 or more metric tons of greenhouse gases, including carbon dioxide, methane and others. Additionally, the Partnership is required to conduct periodic and various facility surveys across its entire system to comply with the EPA's GHG emission calculations and reporting regulations. On December 9, 2014, the EPA published a proposed rule that would expand the petroleum and natural gas system sources for which annual GHG emissions reporting is currently required to include GHG emissions reporting beginning in the 2016 reporting year for certain onshore gathering and boosting systems consisting primarily of gathering pipelines, compressors and process equipment used to perform natural gas compression, dehydration and acid gas removal. In addition, in January 2015, it was announced that the EPA is expected to propose in the summer of 2015 and finalize in 2016 new regulations that will set methane emission standards for new and modified oil and gas production and natural gas processing and transmission facilities as part of an effort to reduce methane emissions from the oil and gas sector by up to 45 percent from 2012 levels by 2025. Some states have also adopted laws regulating GHG emissions, although none of the states in which the Partnership operates have adopted such laws. The federal rules and determinations regarding GHG emissions have not had, and are not expected to have, a material effect on the Partnership's financial condition, results of operations or cash flows.
	Lease Commitments
	The Partnership has various operating lease commitments extending through the year 2024 generally covering office space and equipment rentals. Total lease expense for the years ended December 31, 2014, 2013 and 2012 was approximately $10.7 million, $8.6 million and $6.4 million. The following table summarizes minimum future commitments related to these items at December 31, 2014 (in millions):
	2015	$	4.7
	2016	4.4
	2017	3.9
	2018	3.3
	2019	2.9
	Thereafter	13.6
	Total	$	32.8
	Commitments for Construction
	The Partnership’s future capital commitments are comprised of binding commitments under purchase orders for materials ordered but not received and firm commitments under binding construction service agreements. The commitments as of December 31, 2014, were approximately $61.9 million, all of which are expected to be settled in 2015.
	Pipeline Capacity Agreements
	The Partnership’s operating subsidiaries have entered into pipeline capacity agreements with third-party pipelines that allow the operating subsidiaries to transport gas to off-system markets on behalf of customers. The Partnership incurred expenses of $10.1 million, $9.8 million and $9.1 million related to pipeline capacity agreements for the years ended December 31, 2014, 2013 and 2012. The future commitments related to pipeline capacity agreements as of December 31, 2014, were (in millions):
	2015	$	6.9
	2016	6.3
	2017	6.2
	2018	2
	2019	—
	Thereafter	—
	Total	$	21.4
	Capital Lease
	The Partnership entered into an agreement to lease an office building in Owensboro, Kentucky. The construction of the building was completed and the Partnership took possession of the building in the third quarter 2013, at which time the Partnership recorded a capital lease asset and obligation of $10.5 million. The office building lease has a term of fifteen years with two twenty-year renewal options. Future commitments under this capital lease are as follows (in millions):
	2015	$	1
	2016	1
	2017	1
	2018	1
	2019	1.1
	Thereafter	9.5
	Total minimum lease payments	14.6
	Less amounts representing interest	(4.6		)
	Present value of obligation under capital lease	10
	Less: current portion of obligations under capital lease	(0.4		)
	(recorded in Other current liabilities)
	Long-term obligations under capital lease	$	9.6
	Amortization of the office building under the capital lease for the year ended December 31, 2014 and 2013 was $0.7 million and $0.3 million and was included in Depreciation and amortization. As of December 31, 2014 and 2013, assets recorded in Natural gas transmission and other plant under the capital lease were $10.5 million and the accumulated amortization was $1.0 million and $0.3 million.

Fair_Value_Measurements_Deriva

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI)	12 Months Ended
	Dec. 31, 2014
Disclosure Text Block [Abstract]
Derivative Instruments and Hedging Activities Disclosure [Text Block]	Note 6: Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI)
	The Partnership’s assets and liabilities which are recorded at fair value on a recurring basis are related to outstanding derivatives. At December 31, 2014, the Partnership had no outstanding derivatives recorded in its Consolidated Balance Sheets. At December 31, 2013, the Partnership had $0.5 million of commodity-based derivatives that were recorded in Other current assets. The derivatives were measured using a Level 2 input under the fair value hierarchy.
	In 2014, the assets related to the Bluegrass Project, which included assets held and used and Investment in unconsolidated affiliates, were determined to be impaired and were measured at fair value on a non-recurring basis. As a result, the Partnership recorded an asset impairment charge of $7.1 million and equity losses in unconsolidated affiliates of $85.8 million. Net of controlling interests of $82.9 million, the amount of the loss to the Partnership was $10.0 million. As of December 31, 2014, there was no carrying amounts recorded in the Consolidated Balance Sheets related to the Bluegrass Project. Refer to Note 3 for further information.
Comprehensive Income (Loss) Note [Text Block]	Other Comprehensive Income (OCI)
	The Partnership estimates that approximately $3.5 million of net gains reported in AOCI as of December 31, 2014, are expected to be reclassified into earnings within the next twelve months. This amount is comprised of a $5.9 million increase to earnings related to net periodic benefit cost and a $2.4 million decrease to earnings related to cash flow hedges. The amount related to cash flow hedges are from treasury rate locks used in hedging interest payments associated with debt offerings that were settled in previous periods and are being amortized to earnings over the terms of the related interest payments, generally the terms of the related debt. The following table shows the components and reclassifications to net income of Accumulated other comprehensive loss which is included in Partners' Capital on the Consolidated Balance Sheets for the years ended December 31, 2012 through 2014 (in millions):
		Cash Flow Hedges			Pension and Other Postretirement Benefit Costs			Total
	Beginning balance, January 1, 2012	$	(10.4	)	$	(39.0	)	$	(49.4	)
	Loss recorded in accumulated other comprehensive loss	(7.1		)	—			(7.1		)
	Reclassifications:
	Other operating revenues	(0.1		)	—			(0.1		)
	Interest expense (1)	2.1			—			2.1
	Pension and other postretirement benefit costs	—			(12.8		)	(12.8		)
	Ending balance, December 31, 2012	$	(15.5	)	$	(51.8	)	$	(67.3	)
	Gain recorded in accumulated other comprehensive loss	1.6			—			1.6
	Reclassifications:
	Transportation operating revenues	0.1			—			0.1
	Other operating revenues	(0.1		)	—			(0.1		)
	Disposal of operating assets	(1.2		)	—			(1.2		)
	Interest expense (1)	2.4			—			2.4
	Pension and other postretirement benefit costs	—			0.7			0.7
	Ending balance, December 31, 2013	$	(12.7	)	$	(51.1	)	$	(63.8	)
	Loss recorded in accumulated other comprehensive loss	(0.7		)	—			(0.7		)
	Reclassifications:
	Other operating revenues	0.2			—			0.2
	Interest expense (1)	2.4			—			2.4
	Pension and other postretirement benefit costs	—			(10.9		)	(10.9		)
	Ending balance, December 31, 2014	$	(10.8	)	$	(62.0	)	$	(72.8	)
	-1	Related to amounts deferred in AOCI from Treasury rate locks described above.
Fair Value Disclosures [Text Block]	Financial Assets and Liabilities
	The following methods and assumptions were used in estimating the fair value disclosure amounts for financial assets and liabilities:
	Cash and Cash Equivalents: For cash and short-term financial assets, the carrying amount is a reasonable estimate of fair value due to the short maturity of those instruments.
	Long-Term Debt: The estimated fair value of the Partnership's publicly traded debt is based on quoted market prices at December 31, 2014 and 2013. The fair market value of the debt that is not publicly traded is based on market prices of similar debt at December 31, 2014, and 2013. The carrying amount of the Partnership's variable-rate debt approximated fair value because the instruments bear a floating market-based interest rate.
	The carrying amount and estimated fair values of the Partnership's financial assets and liabilities which were not recorded at fair value on the Consolidated Balance Sheets as of December 31, 2014, and 2013, were as follows (in millions):
	As of December 31, 2014					Estimated Fair Value
	Financial Assets		Carrying Amount			Level 1			Level 2		Level 3		Total
	Cash and cash equivalents		$	6.6		$	6.6		$	—	$	—	$	6.6
	Financial Liabilities
	Long-term debt		$	3,680.10	(1)	$	—		$	3,787.40	$	—	$	3,787.40
	(1) The carrying amount of long-term debt excludes a $9.6 million long-term capital lease obligation.
	As of December 31, 2013					Estimated Fair Value
	Financial Assets		Carrying Amount			Level 1			Level 2		Level 3		Total
	Cash and cash equivalents		$	28.5		$	28.5		$	—	$	—	$	28.5
	Financial Liabilities
	Long-term debt		$	3,414.40	(1)	$	—		$	3,573.80	$	—	$	3,573.80
	(1) The carrying amount of long-term debt excludes a $10.0 million long-term capital lease obligation.

Property_Plant_and_Equipment_P

Property, Plant and Equipment (PPE)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment	Note 7: Property, Plant and Equipment (PPE)
	The following table presents the Partnership’s PPE as of December 31, 2014 and 2013 (in millions):
	Category		2014			Weighted-Average	2013			Weighted-Average
			Amount			Useful Lives	Amount			Useful Lives
						(Years)				(Years)
	Depreciable plant:
	Transmission		$	7,719.80		37	$	7,067.70		37
	Storage		758.5			38	749.7			38
	Gathering		336.7			27	326			27
	General		170			14	160.3			13
	Rights of way and other		114.9			36	111.1			35
	Total utility depreciable plant		9,099.90			37	8,414.80			36
	Non-depreciable:
	Construction work in progress		105.5				174.5
	Storage		105.5				90.8
	Land		28.4				26.9
	Other		16.3				16.3
	Total non-depreciable assets		255.7				308.5
	Total PPE		9,355.60				8,723.30
	Less:  accumulated depreciation		1,766.40				1,489.20
	Total PPE, net		$	7,589.20			$	7,234.10
	The non-depreciable assets were not included in the calculation of the weighted-average useful lives.
	The Partnership holds undivided interests in certain assets, including the Bistineau storage facility of which the Partnership owns 92%, the Mobile Bay Pipeline of which the Partnership owns 64% and offshore and other assets, comprised of pipeline and gathering assets in which the Partnership holds various ownership interests. In addition, the Partnership owns 83% of two ethylene wells and supporting surface facilities in Choctaw, Louisiana, and certain ethylene and propylene pipelines connecting Louisiana Midstream’s storage facilities in Choctaw to chemical manufacturing plants in Geismar, Louisiana.
	The proportionate share of investment associated with these interests has been recorded as PPE on the balance sheets. The Partnership records its portion of direct operating expenses associated with the assets in Operation and maintenance expense. The following table presents the gross PPE investment and related accumulated depreciation for the Partnership’s undivided interests as of December 31, 2014 and 2013 (in millions):
		2014						2013
		Gross PPE			Accumulated Depreciation			Gross PPE			Accumulated Depreciation
		Investment						Investment
	Bistineau storage	$	64.3		$	17.5		$	55.8		$	15.1
	Mobile Bay Pipeline	13			3.6			11.1			3.1
	NGL pipelines and facilities	34.8			2.2			34.8			1.3
	Offshore and other assets	18.8			13.7			19			13.4
	Total	$	130.9		$	37		$	120.7		$	32.9
	Asset Impairment Charges
	The Partnership recognized $10.1 million, $4.1 million and $9.1 million of asset impairment charges for the years ended December 31, 2014, 2013 and 2012.
	Gas Sales
	In 2013, the Partnership recognized a gain of $29.9 million from the sale of approximately 14.9 billion cubic feet of natural gas stored underground with a carrying amount of $26.0 million. The gas was sold to provide capacity for additional parks of customer gas under PAL service as well as a result of a change in the storage gas needed to support operations and no-notice services. The gains related to these gas sales were recorded in Net gain on sale of operating assets.
	Carthage Compressor Station Incident
	In 2011, a fire occurred at one of the Partnership’s compressor stations near Carthage, Texas, which caused significant damage to the compressor building, the compressor units and related equipment housed in the building. The Partnership received a total of $12.3 million in insurance proceeds, of which $0.6 million, $1.7 million and $1.2 million were recorded as a reduction in Operation and maintenance expense for the years ended December 31, 2014, 2013 and 2012.

Goodwill_and_Intangible_Assets

Goodwill and Intangible Assets	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets Disclosure [Text Block]	Note 8: Goodwill and Intangible Assets
	Goodwill
	The Partnership performed its annual goodwill impairment test for its reporting units as of November 30, 2014. The results of the quantitative goodwill impairment test indicated that the fair value of the Partnership’s reporting units significantly exceeded their carrying amounts. No impairment charge related to goodwill was recorded for any of the Partnership’s reporting units during 2014 or 2012. In 2013, the Partnership recognized a goodwill impairment charge of $51.5 million related to the goodwill associated with the Petal acquisition. The fair value of the reporting unit declined from the amount determined in 2012 due primarily to narrowing of natural gas price differentials between time periods, such as winter to summer (time period price spreads) and reduced volatility which negatively affected the value of the Partnership’s storage and PAL services and the cumulative effect of reduced gas price differentials between locations on the pipelines (basis spreads) on the value of the Partnership’s transportation services.
	Changes in the gross amounts of goodwill for the Partnership are summarized as follows (in millions):
	Balance as of January 1, 2013	$	267
	Goodwill impairment charge	(51.5		)
	Balance as of December 31, 2013	215.5
	Acquisition of Boardwalk Petrochemical (1)	21.9
	Balance as of December 31, 2014	$	237.4
	(1) Refer to Note 4 for further information on the acquisition of Boardwalk Petrochemical.
	Intangible Assets
	The following table contains information regarding the Partnership's intangible assets, which includes customer relationships acquired as part of its acquisitions (in millions):
		December 31,
		2014			2013
	Gross carrying amount	$	59.4		$	39.4
	Accumulated amortization	(3.5		)	(2.1		)
	Net carrying amount	$	55.9		$	37.3
	For the year ended December 31, 2014, 2013 and 2012 amortization expense for intangible assets totaled $1.4 million, $1.3 million and $0.8 million and was recorded in Depreciation and amortization on the Consolidated Statements of Income. Amortization expense for the next five years and in total thereafter as of December 31, 2014, is expected to be as follows (in millions):
	2015	$	2
	2016	2
	2017	2
	2018	2
	2019	2
	Thereafter	45.9
		$	55.9
	The weighted-average remaining useful life of the Partnership's intangible assets as of December 31, 2014 was 29 years.

Asset_Retirement_Obligations_A

Asset Retirement Obligations (ARO)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligations (ARO)	Note 9:  Asset Retirement Obligations (ARO)
	The Partnership has identified and recorded legal obligations associated with the abandonment of certain pipeline and storage assets, brine ponds, offshore facilities and the abatement of asbestos consisting of removal, transportation and disposal when removed from certain compressor stations and meter station buildings. Legal obligations exist for the main pipeline and certain other Partnership assets; however, the fair value of the obligations cannot be determined because the lives of the assets are indefinite and therefore cash flows associated with retirement of the assets cannot be estimated with the degree of accuracy necessary to establish a liability for the obligations.
	The following table summarizes the aggregate carrying amount of the Partnership’s ARO (in millions):
		2014			2013
	Balance at beginning of year	$	47.1		$	39
	Liabilities recorded	4.3			8
	Liabilities settled	(6.9		)	(1.7		)
	Accretion expense	1.8			1.8
	Balance at end of year	46.3			47.1
	Less:  Current portion of asset retirement obligations	(6.4		)	(7.8		)
	Long-term asset retirement obligations	$	39.9		$	39.3
	For the Partnership’s operations where regulatory accounting is applicable, depreciation rates for PPE are comprised of two components. One component is based on economic service life (capital recovery) and the other is based on estimated costs of removal (as a component of negative salvage) which is collected in rates and does not represent an existing legal obligation. The Partnership has reflected $60.5 million and $57.6 million as of December 31, 2014 and 2013, in the accompanying Consolidated Balance Sheets as Provision for other asset retirement related to the estimated cost of removal collected in rates.

Regulatory_Assets_and_Liabilit

Regulatory Assets and Liabilities	12 Months Ended
	Dec. 31, 2014
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Assets and Liabilities	Note 10: Regulatory Assets and Liabilities
	The amounts recorded as regulatory assets and liabilities in the Consolidated Balance Sheets as of December 31, 2014 and 2013, are summarized in the table below. The table also includes amounts related to unamortized debt expense and unamortized discount on long-term debt. While these amounts are not regulatory assets and liabilities, they are a critical component of the embedded cost of debt financing utilized in the Texas Gas rate proceedings. The tax effect of the equity component of AFUDC represents amounts recoverable from rate payers for the tax recorded in regulatory accounting. Certain amounts in the table are reflected as a negative, or a reduction, to be consistent with the regulatory books of account. The period of recovery for the regulatory assets included in rates varies from one to eighteen years. The remaining period of recovery for regulatory assets not yet included in rates would be determined in future rate proceedings. None of the regulatory assets shown below were earning a return as of December 31, 2014 and 2013 (in millions):
		2014			2013
	Regulatory Assets:
	Pension	$	10.6		$	10.6
	Tax effect of AFUDC equity	3.5			3.9
	Unamortized debt expense and premium on reacquired debt	9.6			11.5
	Fuel tracker	0.2			0.8
	Total regulatory assets	$	23.9		$	26.8
	Regulatory Liabilities:
	Cashout and fuel tracker	$	0.9		$	1.1
	Provision for other asset retirement	60.5			57.6
	Unamortized discount on long-term debt	(1.5		)	(1.8		)
	Postretirement benefits other than pension	34.2			32.7
	Total regulatory liabilities	$	94.1		$	89.6

Financing

Financing	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Financing	Note 11:  Financing
	Long-Term Debt
	The following table presents all long-term debt issues outstanding as of December 31, 2014 and 2013 (in millions):
		2014				2013
	Notes and Debentures:
	Boardwalk Pipelines
	5.88% Notes due 2016	$	250			$	250
	5.50% Notes due 2017	300				300
	5.20% Notes due 2018	185				185
	5.75% Notes due 2019	350				350
	3.375% Notes due 2023	300				300
	4.95% Notes due 2024 (Boardwalk Pipelines 2024 Notes)	350				—
	Gulf South
	5.05% Notes due 2015 (Gulf South 2015 Notes)	275				275
	6.30% Notes due 2017	275				275
	4.00% Notes due 2022	300				300
	Texas Gas
	4.60% Notes due 2015 (Texas Gas 2015 Notes)	250				250
	4.50% Notes due 2021	440				440
	7.25% Debentures due 2027	100				100
	Total notes and debentures	3,375.00				3,025.00
	Term Loan	200				225
	Revolving Credit Facility:
	Gulf Crossing	120				175
	Capital lease obligation	9.6				10
		3,704.60				3,435.00
	Less: unamortized debt discount	(14.9		)		(10.6		)
	Total Long-Term Debt and Capital Lease Obligation	$	3,689.70			$	3,424.40
	Maturities of the Partnership’s long-term debt for the next five years and in total thereafter are as follows (in millions):
	2015	$	525
	2016	250
	2017	895
	2018	185
	2019	350
	Thereafter	1,490.00
	Total long-term debt	$	3,695.00
	The Partnership has included $525.0 million of debt which matures in less than one year as long-term debt on its balance sheet as of December 31, 2014. The Partnership refinanced the Gulf South 2015 Notes with the issuance of the Boardwalk Pipelines 2024 Notes, which proceeds were used to retire the Gulf South 2015 Notes on February 2, 2015. As of December 31, 2014, the proceeds of the Boardwalk Pipelines 2024 Notes were used to temporarily reduce borrowings under the revolving credit facility until the Gulf South 2015 Notes reached maturity. The Partnership intends to refinance the Texas Gas 2015 Notes due June 1, 2015 on a long-term basis and has adequate available capacity under its revolving credit facility to extend the amount that would otherwise come due in less than a year.
	Notes and Debentures
	As of December 31, 2014 and 2013, the weighted-average interest rate of the Partnership's notes and debentures was 5.31% and 5.32%. For the years ended December 31, 2014, 2013 and 2012, the Partnership completed the following debt issuances (in millions, except interest rates):
	Date of		Issuing Subsidiary		Amount of				Purchaser			Net			Interest		Maturity Date	Interest Payable
	Issuance				Issuance				Discounts			Proceeds			Rate
									and
									Expenses
	Nov-14		Boardwalk Pipelines		$	350			$	7.1		$	342.9	(1)	4.95	%	December 15, 2024	June 15 and December 15
	Nov-12		Boardwalk Pipelines		$	300			$	2.4		$	297.6	(2)	3.375	%	February 1, 2023	February 1 and August 1
	Jun-12		Gulf South		$	300			$	3.5		$	296.5	(3)	4	%	June 15, 2022	June 15 and December 15
	-1	The net proceeds of this offering were used to retire all of the outstanding Gulf South 2015 Notes and the remainder of the net proceeds was used to reduce outstanding borrowings under the Partnership’s revolving credit facility.
	-2	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and repay all amounts outstanding under the subordinated loan agreement that was in place at that time, or $100.0 million.
	-3	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and to redeem $225.0 million of Gulf South's 5.75% notes due August 2012 (2012 Notes) discussed below. BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.
	The Partnership’s notes and debentures are redeemable, in whole or in part, at the Partnership’s option at any time, at a redemption price equal to the greater of 100% of the principal amount of the notes to be redeemed or a “make whole” redemption price based on the remaining scheduled payments of principal and interest discounted to the date of redemption at a rate equal to the Treasury rate plus 20 to 50 basis points depending upon the particular issue of notes, plus accrued and unpaid interest, if any. Other customary covenants apply, including those concerning events of default.
	The indentures governing the notes and debentures have restrictive covenants which provide that, with certain exceptions, neither the Partnership nor any of its subsidiaries may create, assume or suffer to exist any lien upon any property to secure any indebtedness unless the debentures and notes shall be equally and ratably secured. All of the Partnership's debt obligations are unsecured. At December 31, 2014, Boardwalk Pipelines and its operating subsidiaries were in compliance with their debt covenants.
	Redemption of Notes
	In February 2015, the Gulf South 2015 Notes matured and were retired in full. The retirement of this debt was financed through the issuance of the Boardwalk Pipelines 2024 Notes. In August 2012, the 2012 Notes matured and were retired in full. The retirement of this debt was financed through the issuance of the 4.00% Gulf South notes due 2022.
	Revolving Credit Facility
	The Partnership has a revolving credit facility which has aggregate lending commitments of $1.0 billion. Outstanding borrowings under the credit facility as of December 31, 2014, and 2013, were $120.0 million and $175.0 million with a weighted-average borrowing rate of 1.54% and 1.29%. As of February 18, 2015, the Partnership had outstanding borrowings of $460.0 million, resulting in available borrowing capacity of $540.0 million.
	In April 2012, the Partnership entered into a Second Amended and Restated Revolving Credit Agreement (Amended Credit Agreement) with Wells Fargo Bank, N.A., as Administrative Agent, having aggregate lending commitments of $1.0 billion, a maturity date of April 27, 2017, and including Gulf Crossing, Gulf South, Texas Gas, Boardwalk Pipelines and Boardwalk Midstream, LLC, as borrowers. Interest is determined, at the Partnership's election, by reference to (a) the base rate which is the highest of (1) the prime rate, (2) the federal funds rate plus 0.50%, and (3) the one month Eurodollar Rate plus 1.00%, plus an applicable margin, or (b) the LIBOR plus an applicable margin. The applicable margin ranges from 0.00% to 0.875% for loans bearing interest tied to the base rate and ranges from 1.00% to 1.875% for loans bearing interest based on the LIBOR rate, in each case determined based on the individual borrower's credit rating from time to time. The Amended Credit Agreement also provides for a quarterly commitment fee charged on the average daily unused amount of the revolving credit facility ranging from 0.125% to 0.30% and determined based on the individual borrower's credit rating from time to time.
	The credit facility contains various restrictive covenants and other usual and customary terms and conditions, including restrictions regarding the incurrence of additional debt, the sale of assets and sale-leaseback transactions. The financial covenants under the credit facility require the Partnership and its subsidiaries to maintain, among other things, a ratio of total consolidated debt to consolidated EBITDA (as defined in the credit agreement) measured for the previous twelve months of not more than 5.0 to 1.0, or up to 5.5 to 1.0 for the three quarters following an acquisition. The Partnership and its subsidiaries were in compliance with all covenant requirements under the credit facility as of December 31, 2014.
	Term Loan
	The Partnership has a $225.0 million variable-rate term loan due October 1, 2017 (Term Loan), which was used to fund the Louisiana Midstream acquisition. The Term Loan bears interest at a rate that is based on the one-month LIBOR plus an applicable margin. Outstanding borrowings as of December 31, 2014 and 2013, were $200.0 million and $225.0 million, with a weighted-average borrowing interest rate of 1.91% and 1.92%. No additional borrowing capacity is available under the Term Loan.
	Long-Term Debt - Affiliate
	In 2014, the Partnership entered into a Subordinated Loan Agreement with BPHC under which the Partnership can borrow up to $300.0 million (Subordinated Loan) through December 31, 2015. The Subordinated Loan bears interest at increasing rates, ranging 5.75% to 9.75%, payable semi-annually in June and December, commencing December 2014, and maturing in July 2024. The Subordinated Loan must be prepaid with the net cash proceeds from the issuance of additional equity securities by the Partnership or the incurrence of certain indebtedness by the Partnership or its subsidiaries, although BPHC may waive such prepayment. The Subordinated Loan is subordinated in right of payment to the Partnership’s obligations under its revolving credit facility pursuant to the terms of a Subordination Agreement between BPHC and Wells Fargo, N.A., as representative of the lenders under the revolving credit facility. Through the filing date of this Annual Report on Form 10-K, the Partnership has not borrowed any amounts under the Subordinated Loan.
	Common Unit Offering
	For the years ended December 31, 2014, 2013 and 2012, the Partnership completed the following issuances and sales of common units (in millions, except the issuance price):
	Month of Offering		Number of		Issuance		Less Underwriting Discounts and Expenses		Net Proceeds		Common Units Outstanding	Common Units Held by the Public
Common Units			Price		(including General Partner Contribution)				After Offering		After Offering
May-13		12.7		$30.12		$12.30		$376.50		220.3	117.6
Oct-12	(1)	11.2		$26.99		$10.40		$297.60		207.7	105
Aug-12	(1)	11.6		$27.80		$11.20		$317.90		196.5	93.8
Feb-12	(1)	9.2		$27.55		$8.50		$250.20		184.9	82.2
-1	BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.
The proceeds of the May 2013 and August 2012 offerings were used to reduce borrowings under the Partnership’s revolving credit facility; the proceeds of the February 2012 offering were used to purchase the remaining equity interests in Petal; and the proceeds of the October 2012 offering were used to purchase the remaining equity interests in Louisiana Midstream. In addition to funds received from the issuance and sale of common units, the general partner concurrently contributed amounts to maintain its 2% interest in the Partnership.
Summary of Changes in Outstanding Units
The following table summarizes changes in the Partnership’s common and class B units since January 1, 2012 (in millions):
	Common			Class B
	Units			Units(1)
Balance, January 1, 2012	175.7			22.9
Common units issued in connection with underwritten offerings	32			—
Balance, December 31, 2012	207.7			22.9
Common units issued in connection with underwritten offerings	12.7			—
Conversion of class B units	22.9			(22.9	)
Balance, December 31, 2013 and 2014	243.3			—
-1	On October 9, 2013, all of the 22.9 million class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.
Registration Rights Agreement
The Partnership has entered into an Amended and Restated Registration Rights Agreement with BPHC under which the Partnership has agreed to register the resale by BPHC of 27.9 million common units and to reimburse BPHC up to a maximum amount of $0.914 per common unit for underwriting discounts and commissions. As of December 31, 2014 and 2013, the Partnership had an accrued liability of approximately $16.0 million for future underwriting discounts and commissions that would be reimbursed to BPHC and other registration and offering costs that are expected to be incurred by the Partnership.

Employee_Benefits

Employee Benefits	12 Months Ended
	Dec. 31, 2014
Employee Benefits [Abstract]
Employee Benefits	Note 12:  Employee Benefits
	Retirement Plans
	Defined Benefit Retirement Plans
	Texas Gas employees hired prior to November 1, 2006, are covered under a non-contributory, defined benefit pension plan (Pension Plan). The Texas Gas Supplemental Retirement Plan (SRP) provides pension benefits for the portion of an eligible employee’s pension benefit under the Pension Plan that becomes subject to compensation limitations under the Internal Revenue Code. Collectively, the Partnership refers to the Pension Plan and the SRP as Retirement Plans. The Partnership uses a measurement date of December 31 for its Retirement Plans.
	As a result of the Texas Gas rate case settlement in 2006, the Partnership is required to fund the amount of annual net periodic pension cost associated with the Pension Plan, including a minimum of $3.0 million which is the amount included in rates. In each of 2014 and 2013, the Partnership funded $3.0 million to the Pension Plan and expects to fund approximately $3.0 million to the plan in 2015. The Partnership does not anticipate that any Pension Plan assets will be returned to the Partnership during 2015. In 2014 and 2013, there were no payments made under the SRP. The Partnership does not expect to fund the SRP until such time as benefits are paid.
	The Partnership recognizes in expense each year the actuarially determined amount of net periodic pension cost associated with its Retirement Plans, including a minimum amount of $3.0 million related to its Pension Plan, in accordance with the 2006 rate case settlement. Texas Gas is permitted to seek future rate recovery for amounts of annual Pension Plan costs in excess of $6.0 million and is precluded from seeking future recovery of annual Pension Plan costs between $3.0 million and $6.0 million. As a result, the Partnership would recognize a regulatory asset for amounts of annual Pension Plan costs in excess of $6.0 million and would reduce its regulatory asset to the extent that annual Pension Plan costs are less than $3.0 million. Annual Pension Plan costs between $3.0 million and $6.0 million will be charged to expense.
	Postretirement Benefits Other Than Pension (PBOP)
	Texas Gas provides postretirement medical benefits and life insurance to retired employees who were employed full time, hired prior to January 1, 1996, and have met certain other requirements. In each of 2014 and 2013, the Partnership contributed $0.1 million to the PBOP plan. The PBOP plan is currently in an overfunded status; therefore, the Partnership does not expect to make any contributions to the plan in 2015. The Partnership does not anticipate that any plan assets will be returned to the Partnership during 2015. The Partnership uses a measurement date of December 31 for its PBOP plan.
	Projected Benefit Obligation, Fair Value of Assets and Funded Status
	The projected benefit obligation, fair value of assets, funded status and the amounts not yet recognized as components of net periodic pension and postretirement benefits cost for the Retirement Plans and PBOP at December 31, 2014 and 2013, were as follows (in millions):
		Retirement Plans								PBOP
		For the Year Ended								For the Year Ended
		December 31,								December 31,
		2014				2013				2014				2013
	Change in benefit obligation:
	Benefit obligation at beginning of period	$	148.5			$	152.5			$	50			$	59.5
	Service cost	3.9				3.9				0.4				0.5
	Interest cost	5.8				5				2.2				2.1
	Plan participants’ contributions	—				—				0.9				0.8
	Actuarial loss (gain)	3.6				(1.2		)		5.2				(8.3		)
	Benefits paid	(0.5		)		(0.4		)		(3.6		)		(4.6		)
	Settlement	(11.4		)		(11.3		)		—				—
	Benefit obligation at end of period	$	149.9			$	148.5			$	55.1			$	50
	Change in plan assets:
	Fair value of plan assets at beginning of period	$	131.4			$	125.7			$	80.8			$	86.7
	Actual return on plan assets	8.2				14.4				9.1				(2.2		)
	Benefits paid	(0.5		)		(0.4		)		(3.6		)		(4.6		)
	Settlement	(11.4		)		(11.3		)		—				—
	Company contributions	3				3				0.1				0.1
	Plan participants’ contributions	—				—				0.9				0.8
	Fair value of plan assets at end of period	$	130.7			$	131.4			$	87.3			$	80.8
	Funded status	$	(19.2	)		$	(17.1	)		$	32.2			$	30.8
	Items not recognized as components of net periodic cost:
	Prior service cost (credit)	$	—			$	—			$	(8.6	)		$	(16.4	)
	Net actuarial loss	26				24.4				10.7				10.6
	Total	$	26			$	24.4			$	2.1			$	(5.8	)
	At December 31, 2014 and 2013, the following aggregate information relates only to the underfunded plans (in millions):
		Retirement Plans
		For the Year Ended
		December 31,
		2014				2013
	Projected benefit obligation	$	149.9			$	148.5
	Accumulated benefit obligation	139.7				138.4
	Fair value of plan assets	130.7				131.4
	Components of Net Periodic Benefit Cost
	Components of net periodic benefit cost for both the Retirement Plans and PBOP for the years ended December 31, 2014, 2013 and 2012 were as follows (in millions):
		Retirement Plans												PBOP
		For the Year Ended												For the Year Ended
		December 31,												December 31,
		2014				2013				2012				2014				2013			2012
	Service cost	$	3.9			$	3.9			$	4			$	0.4			$	0.5		$	0.5
	Interest cost	5.8				5				5.8				2.2				2.1			2.4
	Expected return on plan assets	(9.5		)		(9.1		)		(8.6		)		(4.2		)		(4.5		)	(4.3		)
	Amortization of prior service credit	—				—				—				(7.8		)		(7.8		)	(7.8		)
	Amortization of unrecognized net loss	1.4				2.1				2.1				0.3				—			0.1
	Settlement charge	1.9				1.7				—				—				—			—
	Net periodic benefit cost	$	3.5			$	3.6			$	3.3			$	(9.1	)		$	(9.7	)	$	(9.1	)
	Due to the Texas Gas rate case settlement in 2006, Texas Gas is permitted to seek future rate recovery for amounts of annual Pension Plan costs in excess of $6.0 million.
	Estimated Future Benefit Payments
	The following table shows benefit payments, which reflect expected future service, as appropriate, which are expected to be paid for both the Retirement Plans and PBOP (in millions):
		Retirement Plans				PBOP
	2015	$	16.3			$	3.1
	2016	15				3.1
	2017	14.8				3.2
2018	15				3.3
2019	15.7				3.3
2020-2024	67.1				16.5
Weighted –Average Assumptions
Weighted-average assumptions used to determine benefit obligations for the years ended December 31, 2014 and 2013, were as follows:
	Retirement Plans												PBOP
	For the Year Ended												For the Year Ended
	December 31,												December 31,
	2014						2013						2014			2013
	Pension			SRP			Pension			SRP
Discount rate	3.35	%		3.75	%		4	%		4.25	%		3.9	%		4.5	%
Expected return on plan assets	7.5	%		7.5	%		7.5	%		7.5	%		5.3	%		5.3	%
Rate of compensation increase	3.5	%		3.5	%		3.5	%		3.5	%		—	%		—	%
Weighted-average assumptions used to determine net periodic benefit cost for the periods indicated were as follows:
	Retirement Plans																	PBOP
	For the Year Ended																	For the Year Ended
	December 31,																	December 31,
	2014						2013					2012						2014		2013			2012
	Pension			SRP			Pension		SRP			Pension			SRP
Discount rate	4	%		4.25	%		3.25%/4.10%	(1)	3.5	%		4.25	%		4.25	%		4.5	%	3.9	%		4.7	%
Expected return on plan assets	7.5	%		7.5	%		7.50%		7.5	%		7.5	%		7.5	%		5.3	%	5.3	%		5.3	%
Rate of compensation increase	3.5	%		3.5	%		3.50%		3.5	%		4	%		4	%		—	%	—	%		—	%
(1) Pension expense was remeasured at September 30, 2013, to reflect a settlement.
The long-term rate of return for plan assets was determined based on widely-accepted capital market principles, long-term return analysis for global fixed income and equity markets as well as the active total return oriented portfolio management style. Long-term trends are evaluated relative to market factors such as inflation, interest rates and fiscal and monetary policies, in order to assess the capital market assumptions as applied to the plan. Consideration of diversification needs and rebalancing is maintained.
PBOP Assumed Health Care Cost Trends
Assumed health care cost trend rates have a significant effect on the amounts reported for PBOP. A one-percentage-point change in assumed trend rates for health care costs would have had the following effects on amounts reported for the year ended December 31, 2014 (in millions):
Effect of 1% Increase:		2014
Benefit obligation at end of year		$	2.2
Total of service and interest costs for year		0.1
Effect of 1% Decrease:
Benefit obligation at end of year		$	(1.9	)
Total of service and interest costs for year		(0.1		)
For measurement purposes, for December 31, 2014, health care cost trend rates for the plans were assumed to remain at 8.0% for 2015-2016, grading down to 5.0% by 2022, assuming 0.5% annual increments for all participants. For December 31, 2013, health care cost trend rates for the plans were assumed to remain at 8.5% for 2014-2015, grading down to 5.0% by 2022, assuming 0.5% annual increments for all participants.
Pension Plan and PBOP Asset Allocation and Investment Strategy
Pension Plan
The Pension Plan investments are held in a trust account and consist of an undivided interest in an investment account of the Loews Corporation Employees Retirement Trust (Master Trust), established by Loews and its participating subsidiaries. Use of the Master Trust permits the commingling of trust assets of the Pension Plan with the assets of the Loews Corporation Cash Balance Retirement Plan for investment and administrative purposes. Although assets of all plans are commingled in the Master Trust, the custodian maintains supporting records for the purpose of allocating the net gain or loss of the investment account to the participating plans. The net investment income of the investment assets is allocated by the custodian to each participating plan based on the relationship of the interest of each plan to the total of the interests of the participating plans. The Master Trust assets are measured at fair value. The fair value of the interest in the assets of the Master Trust associated with the Pension Plan as of December 31, 2014 and 2013, was $130.7 million (or 51.0%) and $131.4 million (or 51.0%), of the total Master Trust assets.
Equity securities are publicly traded securities which are valued using quoted market prices and are considered a Level 1 investment under the fair value hierarchy. Short-term investments that are actively traded or have quoted prices, such as money market funds, are considered a Level 1 investment. Fixed income mutual funds are actively traded and valued using quoted market prices and are considered a Level 1 investment. Corporate and other taxable bonds and asset-backed securities are valued using pricing for similar securities, recently executed transactions, cash flow models with yield curves, broker/dealer quotes and other pricing models utilizing observable inputs and are considered Level 2 investments. The limited partnership and other invested assets consist primarily of hedge funds, whose fair value represents the Master Trust’s share of the net asset value of each company, as determined by the general partner. Level 2 limited partnership and other invested assets include investments which can be redeemed at net asset value in 90 days or less. The limited partnership investments that contain withdrawal provisions greater than 90 days or at the termination of the partnership are considered Level 3 investments.
The following table sets forth by level within the fair value hierarchy a summary of the Master Trust’s investments measured at fair value on a recurring basis at December 31, 2014 (in  millions):
	Master Trust Assets
	Level 1				Level 2				Level 3				Total
Equity securities	$	42.3			$	—			$	—			$	42.3
Short-term investments	11.8				—				—				11.8
Other assets	1.1				—				—				1.1
Fixed income mutual funds	98.7				—				—				98.7
Asset-backed securities	—				6				—				6
Limited partnerships :
Hedge funds	—				56.7				29.5				86.2
Private equity	—				—				10.1				10.1
Total investments	$	153.9			$	62.7			$	39.6			$	256.2
The following table sets forth by level within the fair value hierarchy a summary of the Master Trust’s investments measured at fair value on a recurring basis at December 31, 2013 (in  millions):
	Master Trust Assets
	Level 1				Level 2				Level 3				Total
Equity securities	$	44.6			$	—			$	—			$	44.6
Short-term investments	4.4				—				—				4.4
Other assets	—				3.4				—				3.4
Fixed income mutual funds	100.1				0.3				—				100.4
Asset-backed securities	—				5.8				—				5.8
Limited partnerships:
Hedge funds	—				57.5				29.7				87.2
Private equity	—				—				11.7				11.7
Total investments	$	149.1			$	67			$	41.4			$	257.5
The following table presents a reconciliation of the beginning and ending balances of the fair value measurements using significant unobservable inputs (Level 3) for the Master Trust (in millions):
	Limited				Limited
	Partnerships:				Partnerships:
	Hedge Funds				Private Equity
Balance, January 1, 2013	$	32			$	7.1
Actual return on assets still held	6.2				2.1
Actual return on assets sold	(0.3		)		(0.3		)
Purchases, sales and settlements	(8.2		)		2.8
Net transfers in/(out) of Level 3	—				—
Balance, December 31, 2013	29.7				11.7
Actual return on assets still held	2.1				0.2
Actual return on assets sold	0.1				0.8
Purchases, sales and settlements	(2.4		)		(2.6		)
Net transfers in/(out) of Level 3	—				—
Balance, December 31, 2014	$	29.5			$	10.1
PBOP
The PBOP plan assets are held in a trust and are measured at fair value. Short-term investments that are actively traded or have quoted prices, such as money market or mutual funds, are considered a Level 1 investment. Fixed income mutual funds are actively traded and valued using quoted market prices and are considered Level 1 investments. Tax exempt securities, consisting of municipal securities, corporate and other taxable bonds and asset-backed securities are valued using pricing for similar securities, recently executed transactions, cash flow models with yield curves, broker/dealer quotes and other pricing models utilizing observable inputs and are considered Level 2 investments.
The following table sets forth by level within the fair value hierarchy a summary of the PBOP trust investments measured at fair value on a recurring basis at December 31, 2014 (in  millions):
	PBOP Trust Assets
	Level 1				Level 2				Level 3				Total
Short-term investments	$	3.2			$	—			$	—			$	3.2
Fixed income mutual funds	3				—				—				3
Asset-backed securities	—				20.4				—				20.4
Corporate bonds	—				17.8				—				17.8
Tax exempt securities	—				42.9				—				42.9
Total investments	$	6.2			$	81.1			$	—			$	87.3
The following table sets forth by level within the fair value hierarchy a summary of the PBOP trust investments measured at fair value on a recurring basis at December 31, 2013 (in  millions):
	PBOP Trust Assets
	Level 1				Level 2				Level 3				Total
Short-term investments	$	2.7			$	—			$	—			$	2.7
Fixed income mutual funds	2.8				—				—				2.8
Asset-backed securities	—				19.8				—				19.8
Corporate bonds	—				16.9				—				16.9
Tax exempt securities	—				38.6				—				38.6
Total investments	$	5.5			$	75.3			$	—			$	80.8
Investment strategy
Pension Plan: The Partnership employs a total-return approach using a mix of equities and fixed income investments to maximize the long-term return on plan assets and generate cash flows adequate to meet plan requirements. The intent of this strategy is to minimize plan expenses by outperforming plan liabilities over the long run. Risk tolerance is established through careful consideration of the plan liabilities, plan funded status and corporate financial conditions. The investment strategy has been to allocate between 40% and 60% of the investment portfolio to equity and alternative investments, including limited partnerships, with consideration given to market conditions and target asset returns. The investment portfolio contains a diversified blend of fixed income, equity and short-term securities. Alternative investments, including limited partnerships, have been used to enhance risk adjusted long-term returns while improving portfolio diversification. At December 31, 2014, the pension trust had committed $8.1 million to future capital calls from various third party limited partnership investments in exchange for an ownership interest in the related partnerships. Investment risk is measured and monitored on an ongoing basis through annual liability measurements, periodic asset and liability studies and quarterly investment portfolio reviews.
PBOP: The investment strategy for the PBOP assets is to reduce the volatility of plan investments while protecting the initial investment given the overfunded status of the plan. At December 31, 2014 and 2013, all of the PBOP investments were in fixed income securities.
Defined Contribution Plans
Texas Gas employees hired on or after November 1, 2006, and other employees of the Partnership are provided retirement benefits under a defined contribution money purchase plan. The Partnership also provides 401(k) plan benefits to their employees. Costs related to the Partnership’s defined contribution plans were $9.0 million, $8.6 million and $8.0 million for the years ended December 31, 2014, 2013 and 2012.
Long-Term Incentive Compensation Plans
The Partnership grants to selected employees long-term compensation awards under the LTIP, the Unit Appreciation Right (UAR) and Cash Bonus Plan, and previously made grants under the Strategic Long-Term Incentive Plan (SLTIP). These awards are intended to align the interests of the employees with those of the Partnership’s unitholders, encourage superior performance, attract and retain employees who are essential for the Partnership’s growth and profitability and to encourage employees to devote their best efforts to advancing the Partnership’s business over both long and short-term time horizons. The Partnership also makes annual grants of common units to certain of its directors under the LTIP.
LTIP
The Partnership reserved 3,525,000 common units for grants of units, restricted units, unit options and unit appreciation rights to officers and directors of the Partnership’s general partner and for selected employees under the LTIP. The Partnership has outstanding Phantom Common Units which were granted under the plan. Each such grant: includes a tandem grant of Distribution Equivalent Rights (DERs); vests on the third anniversary of the grant date; and will be payable to the grantee in cash, but may be settled in common units at the discretion of the Partnership’s Board of Directors, upon vesting in an amount equal to the sum of the fair market value of the units (as defined in the plan) that vest on the vesting date, less applicable taxes. The vested amount then credited to the grantee’s DER account is payable only in cash, less applicable taxes. The economic value of the Phantom Common Units is directly tied to the value of the Partnership’s common units, but these awards do not confer any rights of ownership to the grantee. The fair value of the awards will be recognized ratably over the vesting period and remeasured each quarter until settlement based on the market price of the Partnership’s common units and amounts credited under the DERs. The Partnership has not made any grants of units, restricted units, unit options or unit appreciation rights under the plan.
A summary of the status of the Phantom Common Units granted under the Partnership’s LTIP as of December 31, 2014 and 2013, and changes during the years ended December 31, 2014 and 2013, is presented below:
	Phantom Common Units			Total Fair Value				Weighted-Average Vesting Period
				(in millions)				(in years)
Outstanding at January 1, 2013 (1)	192,595			$	4.7			2
Granted	220,808			5.7				2.8
Forfeited	(33,355	)		—				—
Outstanding at December 31, 2013 (1)	380,048			10.9				1.5
Paid	(171,411	)		(3.5		)		—
Forfeited	(8,968	)		—				—
Outstanding at December 31, 2014 (1)	199,669			$	4.1			0.9
-1	Represents fair value and remaining weighted-average vesting period of outstanding awards at the end of the period.
The fair value of the awards at the date of grant was based on the closing market price of the Partnership’s common units on or directly preceding the date of grant. The fair value of the awards at December 31, 2014 and 2013 was based on the closing market price of the common unit on those dates of $17.77 and $25.52 plus the accumulated value of the DERs. The fair value of the awards will be recognized ratably over the vesting period and remeasured each quarter until settlement in accordance with the treatment of awards classified as liabilities. The Partnership recorded $1.2 million, $3.2 million and $1.5 million in Administrative and general expenses during 2014, 2013 and 2012 for the ratable recognition of the fair value of the Phantom Common Unit awards. The total estimated remaining unrecognized compensation expense related to the Phantom Common Units outstanding at December 31, 2014 and 2013, was $1.6 million and $6.1 million.
In 2014 and 2013, the general partner purchased 16,064 and 7,484 of the Partnership’s common units in the open market at a price of $12.51 and $26.72 per unit. These units were granted under the LTIP to the independent directors as part of their director compensation. At December 31, 2014, 3,490,160 units were available for grants under the LTIP.
UAR and Cash Bonus Plan
The UAR and Cash Bonus Plan provides for grants of UARs and Long-Term Cash Bonuses to selected employees of the Partnership. In 2014, the Partnership granted to certain employees $9.2 million of Long-Term Cash Bonuses under the UAR and Cash Bonus Plan. Each Long-Term Cash Bonus will become vested and payable to the holder in cash equal to the amount of the grant after the vesting date. Except in limited circumstances, upon termination of employment during the vesting period, any outstanding and unvested awards of Long-Term Cash Bonuses would be cancelled unpaid. The Partnership recorded compensation expense of $2.6 million, $0.5 million and $0.6 million for the years ended December 31, 2014, 2013 and 2012 related to the Long-Term Cash Bonuses. As of December 31, 2014, there was $6.6 million of total unrecognized compensation cost related to the Long-Term Cash Bonuses.
The economic value of the UARs is tied to the value of the Partnership’s common units, but these awards do not confer any rights of ownership to the grantee. Under the terms of the UAR and Cash Bonus Plan, after the expiration of a restricted period (vesting period) each awarded UAR would become vested and payable in cash to the extent the fair market value (as defined in the plan) of a common unit on such date exceeds the exercise price. Each UAR includes a feature whereby the exercise price is reduced by the amount of any cash distributions made by the Partnership with respect to a common unit during the restricted period (DER Adjustment). Except in limited circumstances, upon termination of employment during the restricted period, any outstanding and unvested awards of UARs would be cancelled unpaid. The fair value of the UARs will be recognized ratably over the vesting period, and will be remeasured each quarter until settlement in accordance with the treatment of awards classified as liabilities.
A summary of the outstanding UARs granted under the Partnership’s UAR and Cash Bonus Plan as of December 31, 2014 and 2013, and changes during 2014 and 2013 is presented below:
	UARs			Weighted- Average				Total Fair Value				Weighted-Average Vesting Period
				Exercise Price				(in millions)				(in years)
Outstanding at January 1, 2013 (1)	605,747			$	29.18			$	1.7			1.4
Paid	(359,148	)
Forfeited	(61,400	)
Granted (2)	293,809			27.57				1.8				2.8
Outstanding at December 31, 2013 (1)	479,008			27.47				1.9				1.5
Vested (3)	(203,168	)
Forfeited	(10,348	)
Outstanding at December 31, 2014 (1)	265,492			$	27.57			$	—			0.9
-1	Represents weighted-average exercise price, remaining weighted-average vesting period and total fair value of outstanding awards at the end of the period.
-2	Represents the weighted-average exercise price and weighted-average vesting period of awards at grant date. The exercise price for each UAR granted was set at $27.57, the closing price of the Partnership’s common units on the New York Stock Exchange on the grant date on February 7, 2013.
-3	Units vested and expired with no value.
The fair value of the UARs was based on the computed value of a call on the Partnership’s common units at the exercise price. The following assumptions were used as inputs to the Black-Scholes valuation model for grants made during 2013. No UARs were granted in 2014.
	Grant Date Assumptions for Grants Made in 2013
Expected life (years)	2.8
Risk free interest rate (1)	0.35%
Expected volatility (2)	32%
-1	Based on the U.S. Treasury yield curve corresponding to the remaining life of the UAR.
-2	Based on the historical volatility of the Partnership’s common units.
Due to the significant decrease in the Partnership’s common unit price in 2014, the Partnership reversed a portion of the previously recognized compensation expense related to the UARs, which resulted in the Partnership recording compensation income of $0.7 million for the year ended December 31, 2014. The Partnership recorded compensation expense of $0.9 million and $0.3 million for the years ended December 31, 2013 and 2012 related to the UARs. As of December 31, 2014, the UARs had no value. As of December 31, 2013, there was $0.9 million of total unrecognized compensation cost related to the non-vested portion of the UARs.
SLTIP
The SLTIP provided for the issuance of up to 500 phantom general partner units (Phantom GP Units) to selected employees of the Partnership and its subsidiaries. The last grant of the Phantom GP Units was made in 2010, which vested and was settled in 2013. No additional grants of Phantom GP units are expected to be made under the SLTIP. The Partnership recorded $0.2 million and $2.3 million in Administrative and general expenses during 2013 and 2012 for the ratable recognition of the fair value of the GP Phantom Unit awards.
A summary of the status of the Partnership’s SLTIP as of December 31, 2014 and 2013, and changes during the years ended December 31, 2014 and 2013, is presented below:
	Phantom GP Units			Total Fair Value				Weighted-Average Vesting Period
				(in millions)				(in years)
Outstanding at January 1, 2013 (1)	145			$	6.9			0.2
Paid	(145	)		(7.2		)		—
Outstanding at December 31, 2013 and 2014	—			$	—			—
-1	Represents fair value and remaining weighted-average vesting period of outstanding awards at the end of the period.
Retention Payment Agreements
In light of challenging market conditions, the need to execute on certain key initiatives and a highly competitive market for talent in the energy industry, in 2014, the Partnership entered into retention payment agreements with certain key employees. The total amount of cash payable under the program would be approximately $12.0 million, subject to the employees remaining employed by the Partnership over a period of three years and other conditions. Each retention payment agreement will vest and become payable in cash as follows: 25% vesting and becoming payable on February 28, 2015, 25% vesting and becoming payable on February 29, 2016, and the remaining 50% vesting and coming payable on February 28, 2017. Except in limited circumstances, upon termination of employment during the vesting period, any outstanding and unvested retention payments would be cancelled unpaid. The Partnership recorded compensation expense of $4.8 million for the year ended December 31, 2014 and as of December 31, 2014, there was $7.0 million of total unrecognized compensation expense related to the retention payment agreements.

Cash_Distributions_and_Net_Inc

Cash Distributions and Net Income per Unit	12 Months Ended
	Dec. 31, 2014
Partners' Capital Notes [Abstract]
Cash Distributions and Net Income per Unit	Note 13:  Cash Distributions and Net Income per Unit
	Cash Distributions
	The Partnership’s cash distribution policy requires that the Partnership distribute to its various ownership interests on a quarterly basis all of its available cash, as defined in its partnership agreement. IDRs, which represent a limited partner ownership interest and are currently held by the Partnership’s general partner, represent the contractual right to receive an increasing percentage of quarterly distributions of available cash as follows:
		Total Quarterly Distribution		Marginal Percentage
				Interest in
				Distributions
		Target Amount		Limited Partner	General
				Unitholders (1)	Partner
					and IDRs
	First Target Distribution	up to $0.4025		98%	2%
	Second Target Distribution	above $0.4025 up to $0.4375		85%	15%
	Third Target Distribution	above $0.4375 up to $0.5250		75%	25%
	Thereafter	above $0.5250		50%	50%
	-1	The class B unitholders participated in distributions on a pari passu basis with the Partnership’s common units up to $0.30 per unit per quarter. The class B units did not participate in quarterly distributions above $0.30 per unit and converted into common units on a one-for-one basis on October 9, 2013.
	The Partnership has declared quarterly distributions per unit to unitholders of record, including holders of common and class B units (through October 9, 2013) and the 2% general partner interest and IDRs held by its general partner as follows (in millions, except distribution per unit):
	Payment Date		Distribution			Amount Paid to Common			Amount Paid			Amount Paid to General Partner (Including IDRs) (1)
			per Unit			Unitholders			to Class B
									Unitholder
	November 20, 2014		$	0.1		$	24.3		$	—		$	0.5
	August 21, 2014		0.1			24.3			—			0.5
	May 15, 2014		0.1			24.3			—			0.5
	February 27, 2014		0.1			24.3			—			0.5
	November 14, 2013		0.5325			129.5			—		(2)	12.4
	August 15, 2013		0.5325			117.3			6.9			11.4
	May 16, 2013		0.5325			110.6			6.8			10.7
	February 28, 2013		0.5325			110.6			6.9			10.8
	November 15, 2012		0.5325			110.6			6.9			10.8
	August 16, 2012		0.5325			104.6			6.9			10.2
	May 17, 2012		0.5325			98.5			6.8			9.6
	February 23, 2012		0.53			98.1			6.8			9.1
	-1	In February 2014, the Partnership decreased its distribution rate to $0.10 per common unit. As a result of the reduced distribution rate, the quarterly target distribution levels for IDR payout were not met and the Partnership paid no amounts with respect to the IDRs in 2014. In 2013 and 2012, the Partnership paid $34.6 million and $30.1 million in distributions on behalf of IDRs.
	-2	On October 9, 2013, all of the 22.9 million Class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.
	In February 2015, the Partnership declared a quarterly cash distribution to unitholders of record of $0.10 per common unit.
	Net Income per Unit
	For purposes of calculating net income per unit, net income for the current period is reduced by the amount of available cash that will be distributed with respect to that period. Any residual amount representing undistributed net income (or loss) is assumed to be allocated to the various ownership interests in accordance with the contractual provisions of the partnership agreement.
	Under the Partnership’s partnership agreement, for any quarterly period, the IDRs participate in net income only to the extent of the amount of cash distributions actually declared, thereby excluding the IDRs from participating in undistributed net income or losses. Accordingly, undistributed net income is assumed to be allocated to the other ownership interests on a pro rata basis, except that the class B units’ participation in net income was limited to $0.30 per unit per quarter. The Class B units were converted to common units on a one-for-one basis in October 2013. Payments made on account of the Partnership’s various ownership interests are determined in relation to actual declared distributions, and are not based on the assumed allocations required under GAAP. Unless noted otherwise, basic and diluted net income per unit are the same.
	The following table provides a reconciliation of net income and the assumed allocation of net income to the common units for purposes of computing net income per unit for the year ended December 31, 2014, (in millions, except per unit data):
		Total			Common			General Partner and IDRs
					Units
	Net income	$	146.8
	Less: Net loss attributable to noncontrolling interests	(86.8		)
	Net income attributable to controlling interests	233.6
	Declared distribution	99.2			$	97.2		$	2
	Assumed allocation of undistributed net income	134.4			131.7			2.7
	Assumed allocation of net income attributable to limited	$	233.6		$	228.9		$	4.7
	partner unitholders and general partner
	Weighted-average units outstanding				243.3
	Net income per unit				$	0.94
	The following table provides a reconciliation of net income and the assumed allocation of net income to the common and class B units for purposes of computing net income per unit for the year ended December 31, 2013. Basic net income per unit is calculated based on the weighted average number of units outstanding for the period. Diluted net income per unit is calculated assuming that the class B units converted on the date that they became convertible, or July 1, 2013 (in millions, except per unit data):
		Total			Common			Class B			General Partner and IDRs
					Units			Units
	Net income	$	250.2
	Less: Net loss attributable to noncontrolling interests	(3.5		)
	Net income attributable to controlling interests	253.7
	Declared distribution	430.5			$	381.8		$	13.7		$	35
	Assumed allocation of undistributed net loss (basic)	(176.8		)	(160.5		)	(12.8		)	(3.5		)
	Assumed allocation of net income attributable to limited	253.7			221.3			0.9			31.5
	partner unitholders and general partner — basic
	Allocation for diluted earnings per unit	—			(4.6		)	4.6			—
	Assumed allocation of net income attributable to limited	$	253.7		$	216.7		$	5.5		$	31.5
	partner unitholders and general partner — diluted
	Weighted-average units outstanding — basic				220.5			17.6
	Weighted-average units outstanding — diluted				226.8			11.3
	Net income per unit — basic				$	1		$	0.05
Net income per unit — diluted				$	0.96		$	0.48
The following table provides a reconciliation of net income and the assumed allocation of net income to the common and class B units for purposes of computing net income per unit for the year ended December 31, 2012 (in millions, except per unit data):
	Total			Common			Class B			General Partner and IDRs
				Units			Units
Net income	$	306
Less: Net loss attributable to predecessor equity	(2.2		)
Net income attributable to limited partner unitholders and	308.2
general partner
Declared distribution	493.1			$	424.3		$	27.5		$	41.3
Assumed allocation of undistributed net loss	(184.9		)	(162.0		)	(19.2		)	(3.7		)
Assumed allocation of net income attributable to limited	$	308.2		$	262.3		$	8.3		$	37.6
partner unitholders and general partner
Weighted-average units outstanding				191.9			22.9
Net income per unit				$	1.37		$	0.36

Income_Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Income Taxes	Note 14:  Income Taxes
	The Partnership is not a taxable entity for federal income tax purposes.  As such, it does not directly pay federal income tax. The Partnership’s taxable income or loss, which may vary substantially from the net income or loss reported in the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. The aggregate difference in the basis of the Partnership’s net assets for financial and income tax purposes cannot be readily determined as the Partnership does not have access to the information about each partner’s tax attributes. The subsidiaries of the Partnership directly incur some income-based state taxes which are presented in Income taxes on the Consolidated Statements of Income.
	Following is a summary of the provision for income taxes for the periods ended December 31, 2014, 2013 and 2012 (in millions):
		For the Year Ended December 31,
		2014		2013		2012
	Current expense:
	State	$	0.3	$	0.4	$	(0.2	)
	Total	0.3		0.4		(0.2		)
	Deferred provision:
	State	0.1		0.1		0.7
	Total	0.1		0.1		0.7
	Income taxes	$	0.4	$	0.5	$	0.5
	The Partnership’s tax years 2011 through 2014 remain subject to examination by the Internal Revenue Service and the states in which it operates. There were no differences between the provision at the statutory rate to the income tax provision at December 31, 2014, 2013 and 2012. As of December 31, 2014 and 2013, there were no significant deferred income tax assets or liabilities.

Credit_Risk

Credit Risk	12 Months Ended
	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Credit Risk	Note 15:  Credit Risk
	Major Customers
	Operating revenues received from the Partnership’s major customer (in millions) and the percentage of total operating revenues earned from that customer were:
		For the Year Ended December 31,
		2014			2013			2012
		Revenue		%	Revenue		%	Revenue		%
	Devon Gas Services, LP	$	120.5	10%	$	127.1	11%	$	133.3	12%
	Gas Loaned to Customers
	Natural gas price volatility can cause changes in credit risk related to gas and NGLs loaned to customers. As of December 31, 2014, the amount of gas owed to the operating subsidiaries due to gas imbalances and gas loaned under PAL agreements was approximately 10.0 trillion British thermal units (TBtu). Assuming an average market price during December 2014 of $3.36 per million British thermal units (MMBtu), the market value of that gas was approximately $33.6 million. As of December 31, 2014, the amount of NGLs owed to the operating subsidiaries due to imbalances was less than 0.1 million barrels, which had a market value of approximately $0.6 million. As of December 31, 2013, the amount of gas owed to the operating subsidiaries due to gas imbalances and gas loaned under PAL agreements was approximately 19.6 TBtu. Assuming an average market price during December 2013 of $4.17 per MMBtu, the market value of this gas at December 31, 2013, would have been approximately $81.7 million. As of December 31, 2013, there were no outstanding imbalances owed to the operating subsidiaries from NGLs. If any significant customer should have credit or financial problems resulting in a delay or failure to repay the gas owed to the operating subsidiaries, it could have a material adverse effect on the Partnership’s financial condition, results of operations or cash flows.

Related_Party_Transactions

Related Party Transactions	12 Months Ended
	Dec. 31, 2014
Related Party Transactions [Abstract]
Related Party Transactions	Note 16:  Related Party Transactions
	Loews provides a variety of corporate services to the Partnership under services agreements, including but not limited to, information technology, tax, risk management, internal audit and corporate development services, plus allocated overheads. The Partnership incurred charges related to these services of $8.8 million, $8.3 million and $8.3 million for the years ended December 31, 2014, 2013 and 2012.
	Distributions paid related to limited partner units held by BPHC and the 2% general partner interest and IDRs held by Boardwalk GP were $52.0 million, $296.8 million and $285.7 million for the years ended December 31, 2014, 2013 and 2012.
	In 2014, the Partnership and BPHC entered into a Subordinated Loan agreement whereby the Partnership can borrow up to $300.0 million. Note 11 contains more information related to the affiliated long-term debt.
	In 2013, the Partnership entered into agreements with BPHC to form two entities for the purpose of investing in the Bluegrass Project. For the years ended December 31, 2014 and 2013, the Partnership contributed $0.8 million and $11.9 million and BPHC contributed $8.2 million and $90.0 million of cash and other assets to these entities. In 2014, the Partnership and BPHC dissolved these entities, resulting in the Partnership receiving $2.2 million in distributions and BPHC receiving $7.9 million in distributions. Refer to Note 3 for further information on the Bluegrass Project.

Recently_Issued_Accounting_Pro

Recently Issued Accounting Pronouncements	12 Months Ended
	Dec. 31, 2014
Text Block [Abstract]
Description of New Accounting Pronouncements Not yet Adopted [Text Block]	Note 17: Recently Issued Accounting Pronouncements
	In May 2014, the Financial Accounting Standards Board issued Accounting Standards Update 2014-09 (ASU 2014-09), Revenue from Contracts with Customers (Topic 606), which will require entities to recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled to in exchange for those goods or services. ASU 2014-09 also requires enhanced disclosures regarding the nature, amount, timing and uncertainty of revenues and cash flows from contracts with customers. ASU 2014-09 is effective for interim and annual reporting periods beginning after December 15, 2016. The Partnership is evaluating the impact, if any, that ASU 2014-09 will have on its financial statements.

Supplemental_Disclosure_of_Cas

Supplemental Disclosure of Cash Flow Information	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Supplemental Disclosure of Cash Flow Information	Note 18:  Supplemental Disclosure of Cash Flow Information (in millions):
		For the Year Ended December 31,
		2014		2013		2012
	Cash paid during the period for:
	Interest (net of amount capitalized) (1)	$	153	$	151	$	169.8
	Income taxes, net	0.1		0.3		0.2
	Non-cash adjustments:
	Accounts payable and PPE	36.9		38.1		37.9
	Capital lease obligations incurred	—		10.5		—
	-1	The 2012 period includes payments of $9.6 million related to the settlements of interest rate derivatives.

Selected_Quarterly_Financial_D

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Selected Quarterly Financial Data (Unaudited)	Note 19:  Selected Quarterly Financial Data (Unaudited)
	The following tables summarize selected quarterly financial data for 2014 and 2013 for the Partnership (in millions, except for earnings per unit):
		2014
		For the Quarter Ended:
		31-Dec			30-Sep			30-Jun			31-Mar
	Operating revenues	$	304.6		$	278.9		$	293.4		$	356.9
	Operating expenses	224.1			210.4			196.9			204.3
	Operating income	80.5			68.5			96.5			152.6
	Interest expense, net	44.2			39.9			40			40.8
	Other (income) expense	(0.6		)	0.1			0.5			86
	Income before income taxes	36.9			28.5			56			25.8
	Income taxes	—			0.1			0.1			0.2
	Net income	36.9			28.4			55.9			25.6
	Net earnings (loss) attributable to	0.1			(0.8		)	(1.5		)	(84.6		)
	noncontrolling interests
	Net income attributable to	$	36.8		$	29.2		$	57.4		$	110.2
	controlling interests
	Net income per unit:	$	0.15		$	0.12		$	0.23		$	0.44
		2013
		For the Quarter Ended:
		31-Dec			30-Sep			30-Jun			31-Mar
	Operating revenues	$	312.9		$	275.5		$	288.7		$	328.5
	Operating expenses	254.4			172.3			177.6			186.8
	Operating income	58.5			103.2			111.1			141.7
	Interest expense, net	41.1			40.9			40.6			40.3
	Other expense (income)	0.5			0.6			—			(0.2		)
	Income before income taxes	16.9			61.7			70.5			101.6
	Income taxes	0.2			—			0.1			0.2
	Net income	16.7			61.7			70.4			101.4
	Net loss attributable to	(2.8		)	(0.6		)	(0.1		)	—
	noncontrolling interests
	Net income attributable to	$	19.5		$	62.3		$	70.5		$	101.4
	controlling interests
	Basic net income per unit:
	Common units	$	0.08		$	0.27		$	0.28		$	0.42
	Class B units	$	(0.02	)	$	(0.32	)	$	0.03		$	0.19
	Diluted net income per unit:
	Common units	$	0.08		$	0.21		$	0.28		$	0.42
	Class B units	$	—		$	—		$	0.03		$	0.19

Guarantee_of_Securities_of_Sub

Guarantee of Securities of Subsidiaries	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Guarantee of Securities of Subsidiaries	Note 20:  Guarantee of Securities of Subsidiaries
	Boardwalk Pipelines (subsidiary issuer) has issued securities which have been fully and unconditionally guaranteed by the Partnership (parent guarantor). The Partnership's subsidiaries have no significant restrictions on their ability to pay distributions or make loans to the Partnership except as noted in the debt covenants and have no restricted assets at December 31, 2014 and 2013. Note 11 contains additional information regarding the Partnership's debt and related covenants.
	Condensed Consolidating Balance Sheets as of December 31, 2014
	(Millions)
	Assets		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer
	Cash and cash equivalents		$	0.5		$	1.8		$	4.3		$	—			$	6.6
	Receivables		—			—			110.9			—				110.9
	Receivables - affiliate		—			—			9			(9.0		)		—
	Gas and liquids stored underground		—			—			4.1			—				4.1
	Prepayments		0.1			—			14.4			—				14.5
	Advances to affiliates		—			6.3			106.2			(112.5		)		—
	Other current assets		0.5			—			19.2			(6.2		)		13.5
	Total current assets		1.1			8.1			268.1			(127.7		)		149.6
	Investment in consolidated subsidiaries		1,970.60			6,744.10			—			(8,714.7		)		—
	Property, plant and equipment, gross		0.6			—			9,355.00			—				9,355.60
	Less–accumulated depreciation and		0.6			—			1,765.80			—				1,766.40
	amortization
	Property, plant and equipment, net		—			—			7,589.20			—				7,589.20
	Other noncurrent assets		—			3.4			465.2			(0.6		)		468
	Advances to affiliates – noncurrent		2,148.30			212			996.5			(3,356.8		)		—
	Total other assets		2,148.30			215.4			1,461.70			(3,357.4		)		468
	Total Assets		$	4,120.00		$	6,967.60		$	9,319.00		$	(12,199.8	)		$	8,206.80
	Liabilities and Equity		Parent			Subsidiary			Non-guarantor			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer			Subsidiaries
	Payables		$	0.2		$	0.1		$	61.8		$	—			$	62.1
	Payable to affiliates		1.5			—			9			(9.0		)		1.5
	Advances from affiliates		—			106.2			6.3			(112.5		)		—
	Other current liabilities		—			21.4			141.7			(6.5		)		156.6
	Total current liabilities		1.7			127.7			218.8			(128.0		)		220.2
	Total long-term debt and capital lease		—			1,724.50			1,965.20			—				3,689.70
	obligation
	Payable to affiliate - noncurrent		16			—			—			—				16
	Advances from affiliates - noncurrent		—			3,144.80			212			(3,356.8		)		—
	Other noncurrent liabilities		—			—			178.9			(0.3		)		178.6
	Total other liabilities and deferred		16			3,144.80			390.9			(3,357.1		)		194.6
	credits
	Total partners’ capital		4,102.30			1,970.60			6,744.10			(8,714.7		)		4,102.30
	Noncontrolling interest		—			—			—			—				—
	Total Equity		4,102.30			1,970.60			6,744.10			(8,714.7		)		4,102.30
	Total Liabilities and Equity		$	4,120.00		$	6,967.60		$	9,319.00		$	(12,199.8	)		$	8,206.80
	Condensed Consolidating Balance Sheets as of December 31, 2013
	(Millions)
	Assets		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer
	Cash and cash equivalents		$	0.2		$	9.2		$	19.1		$	—			$	28.5
	Receivables		—			—			119.2			—				119.2
	Receivables - affiliate		0.1			0.1			14.3			(13.4		)		1.1
	Gas and liquids stored underground		—			—			0.7			—				0.7
	Prepayments		0.3			—			12.6			—				12.9
	Advances to affiliates		—			—			194.4			(194.4		)		—
	Other current assets		—			—			23.8			(9.1		)		14.7
	Total current assets		0.6			9.3			384.1			(216.9		)		177.1
	Investment in consolidated subsidiaries		1,480.80			6,138.30			—			(7,619.1		)		—
	Property, plant and equipment, gross		0.6			—			8,722.70			—				8,723.30
	Less–accumulated depreciation		0.6			—			1,488.60			—				1,489.20
	and amortization
	Property, plant and equipment, net		—			—			7,234.10			—				7,234.10
	Other noncurrent assets		0.3			3.7			420.7			—				424.7
	Advances to affiliates – noncurrent		2,512.10			168.7			733.1			(3,413.9		)		—
	Investment in unconsolidated affiliates		—			—			78.6			—				78.6
	Total other assets		2,512.40			172.4			1,232.40			(3,413.9		)		503.3
	Total Assets		$	3,993.80		$	6,320.00		$	8,850.60		$	(11,249.9	)		$	7,914.50
	Liabilities and Equity		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
Guarantor			Issuer
Payables		$	0.2		$	—		$	70.6		$	—			$	70.8
Payable to affiliates		0.7			—			13.9			(13.4		)		1.2
Advances from affiliates		—			194.4			—			(194.4		)		—
Other current liabilities		—			19.7			153.3			(9.0		)		164
Total current liabilities		0.9			214.1			237.8			(216.8		)		236
Total long-term debt and capital lease		—			1,379.90			2,044.50			—				3,424.40
obligation
Payable to affiliate - noncurrent		16			—			—			—				16
Advances from affiliates - noncurrent		—			3,245.20			168.7			(3,413.9		)		—
Other noncurrent liabilities		—			—			174.8			(0.1		)		174.7
Total other liabilities and deferred		16			3,245.20			343.5			(3,414.0		)		190.7
credits
Total partners’ capital		3,976.90			1,480.80			6,138.30			(7,619.1		)		3,976.90
Noncontrolling interest		—			—			86.5			—				86.5
Total Equity		3,976.90			1,480.80			6,224.80			(7,619.1		)		4,063.40
Total Liabilities and Equity		$	3,993.80		$	6,320.00		$	8,850.60		$	(11,249.9	)		$	7,914.50
Condensed Consolidating Statements of Income for the Year Ended December 31, 2014
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Operating Revenues:
Transportation	$	—		$	—		$	1,157.90		$	(92.8	)		$	1,065.10
Parking and lending	—			—			23.3			—				23.3
Storage	—			—			90.4			(0.9		)		89.5
Other	—			—			55.9			—				55.9
Total operating revenues	—			—			1,327.50			(93.7		)		1,233.80
Operating Costs and Expenses:
Fuel and transportation	—			—			214.4			(93.7		)		120.7
Operation and maintenance	—			—			198.8			—				198.8
Administrative and general	0.2			—			124.8			—				125
Other operating costs and expenses	0.2			—			391			—				391.2
Total operating costs and expenses	0.4			—			929			(93.7		)		835.7
Operating (loss) income	(0.4		)	—			398.5			—				398.1
Other Deductions (Income):
Interest expense	—			76.5			89			—				165.5
Interest (income) expense - affiliates, net	(30.0		)	41.2			(11.2		)	—				—
Interest income	—			—			(0.6		)	—				(0.6		)
Equity in earnings of subsidiaries	(204.0		)	(321.7		)	—			525.7				—
Equity losses in unconsolidated	—			—			86.5			—				86.5
affiliates
Miscellaneous other income, net	—			—			(0.5		)	—				(0.5		)
Total other (income) deductions	(234.0		)	(204.0		)	163.2			525.7				250.9
Income (loss) before income taxes	233.6			204			235.3			(525.7		)		147.2
Income taxes	—			—			0.4			—				0.4
Net income (loss)	233.6			204			234.9			(525.7		)		146.8
Net loss attributable to noncontrolling	—			—			(86.8		)	—				(86.8		)
interests
Net income (loss) attributable to controlling	$	233.6		$	204		$	321.7		$	(525.7	)		$	233.6
interests
Condensed Consolidating Statements of Income for the Year Ended December 31, 2013
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Operating Revenues:
Transportation	$	—		$	—		$	1,116.40		$	(88.4	)		$	1,028.00
Parking and lending	—			—			24			(0.1		)		23.9
Storage	—			—			111			(0.1		)		110.9
Other	—			—			42.8			—				42.8
Total operating revenues	—			—			1,294.20			(88.6		)		1,205.60
Operating Costs and Expenses:
Fuel and transportation	—			—			182			(88.6		)		93.4
Operation and maintenance	—			0.3			186.2			—				186.5
Administrative and general	(0.1		)	0.8			116.7			—				117.4
Other operating costs and expenses	0.3			0.1			393.4			—				393.8
Total operating costs and expenses	0.2			1.2			878.3			(88.6		)		791.1
Operating (loss) income	(0.2		)	(1.2		)	415.9			—				414.5
Other Deductions (Income):
Interest expense	—			72.7			90.7			—				163.4
Interest (income) expense - affiliates, net	(33.6		)	41.3			(7.7		)	—				—
Interest income	—			—			(0.5		)	—				(0.5		)
Equity in earnings of subsidiaries	(220.3		)	(335.5		)	—			555.8				—
Equity losses in unconsolidated affiliates	—			—			1.2			—				1.2
Miscellaneous other income, net	—			—			(0.3		)	—				(0.3		)
Total other (income) deductions	(253.9		)	(221.5		)	83.4			555.8				163.8
Income (loss) before income taxes	253.7			220.3			332.5			(555.8		)		250.7
Income taxes	—			—			0.5			—				0.5
Net income (loss)	253.7			220.3			332			(555.8		)		250.2
Net loss attributable to noncontrolling	—			—			(3.5		)	—				(3.5		)
interests
Net income (loss) attributable to controlling	$	253.7		$	220.3		$	335.5		$	(555.8	)		$	253.7
interests
Condensed Consolidating Statements of Income for the Year Ended December 31, 2012
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Operating Revenues:
Transportation	$	—		$	—		$	1,147.50		$	(89.2	)		$	1,058.30
Parking and lending	—			—			28.7			(0.7		)		28
Storage	—			—			85.4			(0.7		)		84.7
Other	—			—			14			—				14
Total operating revenues	—			—			1,275.60			(90.6		)		1,185.00
Operating Costs and Expenses:
Fuel and transportation	—			—			170			(90.6		)		79.4
Operation and maintenance	—			—			167.2			—				167.2
Administrative and general	0.5			—			114.8			—				115.3
Other operating costs and expenses	0.3			—			349			—				349.3
Total operating costs and expenses	0.8			—			801			(90.6		)		711.2
Operating (loss) income	(0.8		)	—			474.6			—				473.8
Other Deductions (Income):
Interest expense	—			63.1			98.4			—				161.5
Interest (income) expense - affiliates, net	(35.6		)	52.9			(10.4		)	—				6.9
Interest income	—			—			(0.7		)	—				(0.7		)
Equity in earnings of subsidiaries	(271.2		)	(387.2		)	—			658.4				—
Miscellaneous other income, net	—			—			(0.4		)	—				(0.4		)
Total other (income) deductions	(306.8		)	(271.2		)	86.9			658.4				167.3
Income (loss) before income taxes	306			271.2			387.7			(658.4		)		306.5
Income taxes	—			—			0.5			—				0.5
Net income (loss)	306			271.2			387.2			(658.4		)		306
Net loss attributable to noncontrolling	—			—			—			—				—
interests
Net income (loss) attributable to controlling	$	306		$	271.2		$	387.2		$	(658.4	)		$	306
interests
Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2014
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net income (loss)	$	233.6		$	204		$	234.9		$	(525.7	)		$	146.8
Other comprehensive income (loss):
(Loss) gain on cash flow hedges	(0.7		)	(0.7		)	(0.7		)	1.4				(0.7		)
Reclassification adjustment transferred to	2.6			2.6			0.9			(3.5		)		2.6
Net income from cash flow hedges
Pension and other postretirement	(10.9		)	(10.9		)	(10.9		)	21.8				(10.9		)
benefit costs
Total Comprehensive Income (Loss)	224.6			195			224.2			(506.0		)		137.8
Comprehensive loss attributable to	—			—			(86.8		)	—				(86.8		)
noncontrolling interests
Comprehensive income (loss)	$	224.6		$	195		$	311		$	(506.0	)		$	224.6
attributable to controlling interests
Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2013
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net income (loss)	$	253.7		$	220.3		$	332		$	(555.8	)		$	250.2
Other comprehensive income (loss):
Gain (loss) on cash flow hedges	1.6			1.6			1.6			(3.2		)		1.6
Reclassification adjustment transferred to	1.2			1.2			(0.5		)	(0.7		)		1.2
Net income from cash flow hedges
Pension and other postretirement	0.7			0.7			0.7			(1.4		)		0.7
benefit costs
Total Comprehensive Income (Loss)	257.2			223.8			333.8			(561.1		)		253.7
Comprehensive loss attributable to	—			—			(3.5		)	—				(3.5		)
noncontrolling interests
Comprehensive income (loss)	$	257.2		$	223.8		$	337.3		$	(561.1	)		$	257.2
attributable to controlling interests
Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2012
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net income (loss)	$	306		$	271.2		$	387.2		$	(658.4	)		$	306
Other comprehensive income (loss):
(Loss) gain on cash flow hedges	(7.1		)	(7.1		)	(6.7		)	13.8				(7.1		)
Reclassification adjustment transferred to	2			2			0.3			(2.3		)		2
Net Income from cash flow hedges
Pension and other postretirement	(12.8		)	(12.8		)	(12.8		)	25.6				(12.8		)
benefit costs
Total Comprehensive Income (Loss)	288.1			253.3			368			(621.3		)		288.1
Comprehensive loss attributable to	—			—			—			—				—
noncontrolling interests
Comprehensive income (loss) attributable to	$	288.1		$	253.3		$	368		$	(621.3	)		$	288.1
controlling interests
Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2014
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net cash provided by (used in)	$	30.2		$	(112.1	)	$	595.5		$	—			$	513.6
operating activities
INVESTING ACTIVITIES:
Capital expenditures	—			—			(404.4		)	—				(404.4		)
Proceeds from sale of operating assets	—			—			2.9			—				2.9
Proceeds from insurance and other	—			—			6.3			—				6.3
recoveries
Advances to affiliates, net	363.9			(49.6		)	(175.2		)	(139.0		)		0.1
Investment in unconsolidated affiliates	—			—			(20.5		)	—				(20.5		)
Distribution from unconsolidated	—			—			11.1			—				11.1
affiliates
Acquisition of businesses, net of cash	(294.7		)	—			—			—				(294.7		)
acquired
Net cash provided by (used in)	69.2			(49.6		)	(579.8		)	(139.0		)		(699.2		)
investing activities
FINANCING ACTIVITIES:
Proceeds from long-term debt, net of issuance cost	—			342.9			—			—				342.9
Proceeds from borrowings on revolving	—			—			665			—				665
credit agreement
Repayment of borrowings on revolving	—			—			(720.0		)	—				(720.0		)
credit agreement
Repayment of borrowings from term	—			—			(25.0		)	—				(25.0		)
loan
Principal payment of capital lease	—			—			(0.4		)	—				(0.4		)
obligation
Advances from affiliates, net	0.1			(188.6		)	49.6			139				0.1
Distributions paid	(99.2		)	—			—			—				(99.2		)
Capital contribution from noncontrolling	—			—			8.2			—				8.2
interests
Distributions paid to noncontrolling	—			—			(7.9		)	—				(7.9		)
interests
Net cash (used in) provided by	(99.1		)	154.3			(30.5		)	139				163.7
financing activities
Increase (decrease) in cash and cash equivalents	0.3			(7.4		)	(14.8		)	—				(21.9		)
Cash and cash equivalents at	0.2			9.2			19.1			—				28.5
beginning of period
Cash and cash equivalents at	$	0.5		$	1.8		$	4.3		$	—			$	6.6
end of period
Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2013
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net cash provided by (used in)	$	33.9		$	(108.8	)	$	609.2		$	—			$	534.3
operating activities
INVESTING ACTIVITIES:
Capital expenditures	—			—			(294.8		)	—				(294.8		)
Proceeds from sale of operating assets	—			—			60.7			—				60.7
Proceeds from insurance and other	—			—			1.4			—				1.4
recoveries
Advances to affiliates, net	126.4			(84.3		)	(342.8		)	300.7				—
Investment in consolidated affiliates	—			(15.1		)	—			15.1				—
Investment in unconsolidated affiliates	—			—			(76.7		)	—				(76.7		)
Net cash provided by (used in)	126.4			(99.4		)	(652.2		)	315.8				(309.4		)
investing activities
FINANCING ACTIVITIES:
Proceeds from borrowings on revolving	—			—			1,128.00			—				1,128.00
credit agreement
Repayment of borrowings on revolving	—			—			(1,255.0		)	—				(1,255.0		)
credit agreement
Contribution from parent	—			—			15.1			(15.1		)		—
Principal payment of capital lease	—			—			(0.2		)	—				(0.2		)
obligation
Advances from affiliates, net	(2.8		)	216.4			84.3			(300.7		)		(2.8		)
Distributions paid	(533.9		)	—			—			—				(533.9		)
Capital contribution from noncontrolling	—			—			87.1			—				87.1
interests
Proceeds from sale of common units	368.7			—			—			—				368.7
Capital contribution from general partner	7.8			—			—			—				7.8
Net cash (used in) provided by	(160.2		)	216.4			59.3			(315.8		)		(200.3		)
financing activities
Increase in cash and cash equivalents	0.1			8.2			16.3			—				24.6
Cash and cash equivalents at	0.1			1			2.8			—				3.9
beginning of period
Cash and cash equivalents at	$	0.2		$	9.2		$	19.1		$	—			$	28.5
end of period
Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2012
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net cash provided by (used in)	$	31.4		$	577.9		$	655.7		$	(689.5	)		$	575.5
operating activities
INVESTING ACTIVITIES:
Capital expenditures	—			—			(226.9		)	—				(226.9		)
Proceeds from sale of operating assets	—			—			5.9			—				5.9
Proceeds from insurance and other	—			—			10.4			—				10.4
recoveries
Advances to affiliates, net	(404.2		)	(84.4		)	66.2			422.4				—
Investment in consolidated affiliates	(17.0		)	(398.0		)	—			415				—
Acquisition of businesses, net of cash	—			—			(620.2		)	—				(620.2		)
acquired
Net cash (used in) provided by	(421.2		)	(482.4		)	(764.6		)	837.4				(830.8		)
investing activities
FINANCING ACTIVITIES:
Proceeds from long-term debt and term	—			297.6			520.4			—				818
loans
Repayment of borrowings from	—			(100.0		)	(425.0		)	—				(525.0		)
long-term debt, term loans and
subordinated debt
Proceeds from borrowings on revolving	—			300			1,835.00			—				2,135.00
credit agreement
Repayment of borrowings on revolving	—			(403.8		)	(1,891.5		)	—				(2,295.3		)
credit agreement including financing
costs
Contribution from parent	—			17			398			(415.0		)		—
Contribution received related to	—			—			269.2			—				269.2
predecessor equity
Repayment of contribution received	—			(554.0		)	—			—				(554.0		)
related to predecessor equity
Advances from affiliate	2.6			338			84.4			(422.4		)		2.6
Distributions paid	(478.9		)	—			(689.5		)	689.5				(478.9		)
Proceeds from sale of common units	847.7			—			—			—				847.7
Capital contribution from general	18			—			—			—				18
partner
Net cash provided by (used in)	389.4			(105.2		)	101			(147.9		)		237.3
financing activities
Decrease in cash and cash equivalents	(0.4		)	(9.7		)	(7.9		)	—				(18.0		)
Cash and cash equivalents at	0.5			10.7			10.7			—				21.9
beginning of period
Cash and cash equivalents at	$	0.1		$	1		$	2.8		$	—			$	3.9
end of period

Schedule_II_Valuation_and_Qual

Schedule II Valuation and Qualifying Accounts	12 Months Ended
	Dec. 31, 2014
Disclosure Text Block [Abstract]
Schedule of Valuation and Qualifying Accounts Disclosure [Text Block]	Valuation and Qualifying Accounts
	The following table presents those accounts that have a reserve as of December 31, 2014, 2013 and 2012 and are not included in specific schedules herein. These amounts have been deducted from the respective assets on the Consolidated Balance Sheets (in millions):
				Additions
	Description	Balance at		Charged to Costs and Expenses			Other Additions		Deductions		Balance at
		Beginning of Period									End of Period
	Allowance for doubtful accounts:
	2014	$	—	$	—		$	—	$	—	$	—
	2013	0.2		(0.2		)	—		—		—
	2012	0.2		—			—		—		0.2

Accounting_Policies_Policies

Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Consolidation, Policy [Policy Text Block]	Principles of Consolidation
	The consolidated financial statements include the Partnership’s accounts and those of its wholly-owned subsidiaries after elimination of intercompany transactions. The Partnership also consolidates variable interest entities (VIEs) in which the Partnership is the primary beneficiary. Third party or affiliate ownership interests in the Partnership's subsidiaries and consolidated VIEs are presented as noncontrolling interests.
	The Partnership applies the equity method of accounting for investments in unconsolidated affiliates in which it owns 20 percent to 50 percent of the voting interests or otherwise exercises significant influence, but not control, over operating and financial policies of the investee. Under this method, the carrying amounts of the Partnership's equity investments are increased by a proportionate share of the investee's net income and contributions made, and decreased by a proportionate share of the investee's net losses and distributions received.
Use of Estimates, Policy [Policy Text Block]	Use of Estimates
	The preparation of financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues, expenses and disclosure of contingent assets and liabilities and the fair values of certain items. The Partnership bases its estimates on historical experience and on various other assumptions that are believed to be reasonable under the circumstances, which form the basis for making judgments about the carrying amounts of assets and liabilities that are not readily apparent from other sources. Actual results could differ from such estimates.
Segment Reporting, Policy [Policy Text Block]	Segment Information
	The Partnership operates in one reportable segment - the operation of interstate natural gas and NGLs pipeline systems including integrated storage facilities. This segment consists of interstate natural gas pipeline systems which originate in the Gulf Coast region, Oklahoma and Arkansas, and extend north and east through the Midwestern states of Tennessee, Kentucky, Illinois, Indiana and Ohio and NGLs pipelines and storage facilities in Louisiana and Texas.
Public Utilities, Policy [Policy Text Block]	Regulatory Accounting
	Most of the Partnership's natural gas pipeline subsidiaries are regulated by the Federal Energy Regulatory Commission (FERC). When certain criteria are met, GAAP requires that certain rate-regulated entities account for and report assets and liabilities consistent with the economic effect of the manner in which independent third-party regulators establish rates (regulatory accounting). This basis of accounting is applicable to operations of the Partnership’s Texas Gas subsidiary which records certain costs and benefits as regulatory assets and liabilities in order to provide for recovery from or refund to customers in future periods, but is not applicable to operations associated with the Fayetteville and Greenville Laterals due to rates charged under negotiated rate agreements and a portion of the storage capacity due to the regulatory treatment associated with the rates charged for that capacity. Regulatory accounting is not applicable to the Partnership’s other FERC-regulated entities.
	The Partnership monitors the regulatory and competitive environment in which it operates to determine that its regulatory assets continue to be probable of recovery. If the Partnership were to determine that all or a portion of its regulatory assets no longer met the criteria for recognition as regulatory assets, that portion which was not recoverable would be written off, net of any regulatory liabilities.
	Note 10 contains more information regarding the Partnership’s regulatory assets and liabilities.
Fair Value Measurement, Policy [Policy Text Block]	Fair Value Measurements
	Fair value refers to an exit price that would be received to sell an asset or paid to transfer a liability in an orderly transaction in the principal market in which the reporting entity transacts based on the assumptions market participants would use when pricing the asset or liability assuming its highest and best use. A fair value hierarchy has been established that prioritizes the information used to develop those assumptions giving priority, from highest to lowest, to quoted prices in active markets for identical assets and liabilities (Level 1); observable inputs not included in Level 1, for example, quoted prices for similar assets and liabilities (Level 2); and unobservable data (Level 3), for example, a reporting entity’s own internal data based on the best information available in the circumstances. The Partnership uses fair value measurements to record derivatives, asset retirement obligations and impairments. Fair value measurements are also used to perform goodwill impairment testing and report fair values for certain items contained in this Report. The Partnership considers any transfers between levels within the fair value hierarchy to have occurred at the beginning of a quarterly reporting period.  The Partnership did not recognize any transfers between Level 1 and Level 2 of the fair value hierarchy and did not change its valuation techniques or inputs during the year ended December 31, 2014.
	Notes 6 and 12 contain more information regarding fair value measurements.
Cash and Cash Equivalents, Policy [Policy Text Block]	Cash and Cash Equivalents
	Cash equivalents are highly liquid investments with an original maturity of three months or less and are stated at cost plus accrued interest, which approximates fair value. The Partnership had no restricted cash at December 31, 2014 and 2013.
Cash Management [Policy Text Block]	Cash Management
	The operating subsidiaries participate in an intercompany cash management program with those that are FERC-regulated participating to the extent they are permitted under FERC regulations. Under the cash management program, depending on whether a participating subsidiary has short-term cash surpluses or cash requirements, Boardwalk Pipelines either provides cash to them or they provide cash to Boardwalk Pipelines. The transactions are represented by demand notes and are stated at historical carrying amounts. Interest income and expense is recognized on an accrual basis when collection is reasonably assured. The interest rate on intercompany demand notes is London Interbank Offered Rate (LIBOR) plus one percent and is adjusted every three months.
Trade and Other Accounts Receivable, Policy [Policy Text Block]	Trade and Other Receivables
	Trade and other receivables are stated at their historical carrying amount, net of allowances for doubtful accounts. The Partnership establishes an allowance for doubtful accounts on a case-by-case basis when it believes the required payment of specific amounts owed is unlikely to occur. Uncollectible receivables are written off when a settlement is reached for an amount that is less than the outstanding historical balance or a receivable amount is deemed otherwise unrealizable.
Gas Stored Underground and Gas Receivables and Payables [Policy Text Block]	Gas Stored Underground and Gas Receivables and Payables
	Certain of the Partnership's operating subsidiaries have underground gas in storage which is utilized for system management and operational balancing, as well as for services including firm and interruptible storage associated with certain no-notice and parking and lending (PAL) services. Gas stored underground includes the historical cost of natural gas volumes owned by the operating subsidiaries, at times reduced by certain operational encroachments upon that gas. Current gas stored underground represents net retained fuel remaining after providing transportation and storage services which is available for resale and is valued at the lower of weighted-average cost or market.
	The operating subsidiaries provide storage services whereby they store natural gas or NGLs on behalf of customers and also periodically hold customer gas under PAL services. Since the customers retain title to the gas held by the Partnership in providing these services, the Partnership does not record the related gas on its balance sheet. Certain of the Partnership's operating subsidiaries also periodically lend gas and NGLs to customers.
	In the course of providing transportation and storage services to customers, the operating subsidiaries may receive different quantities of gas from shippers and operators than the quantities delivered on behalf of those shippers and operators. This results in transportation and exchange gas receivables and payables, commonly known as imbalances, which are settled in cash or the receipt or delivery of gas in the future. Settlement of imbalances requires agreement between the pipelines and shippers or operators as to allocations of volumes to specific transportation contracts and timing of delivery of gas based on operational conditions.  The receivables and payables are valued at market price for operations where regulatory accounting is not applicable and are valued at the historical value of gas in storage for operations where regulatory accounting is applicable.
Materials and Supplies [Policy Text Block]	Materials and Supplies
	Materials and supplies are carried at average cost and are included in Other Assets on the Consolidated Balance Sheets. The Partnership expects its materials and supplies to be used for capital projects related to its property, plant and equipment and for future growth projects. At December 31, 2014 and 2013, the Partnership held approximately $15.3 million and $12.8 million of materials and supplies which were reflected in Other Assets on the Consolidated Balance Sheets.
Property, Plant and Equipment, Policy [Policy Text Block]	Property, Plant and Equipment (PPE) and Repair and Maintenance Costs
	PPE is recorded at its original cost of construction or fair value of assets purchased. Construction costs and expenditures for major renewals and improvements which extend the lives of the respective assets are capitalized. Construction work in progress is included in the financial statements as a component of PPE. All repair and maintenance costs are expensed as incurred.
	Depreciation of PPE related to operations for which regulatory accounting does not apply is provided for using the straight-line method of depreciation over the estimated useful lives of the assets, which range from 3 to 35 years. The ordinary sale or retirement of PPE for these assets could result in a gain or loss. Depreciation of PPE related to operations for which regulatory accounting is applicable is provided for primarily on the straight-line method at FERC-prescribed rates over estimated useful lives of 5 to 62 years. Reflecting the application of composite depreciation, gains and losses from the ordinary sale or retirement of PPE for these assets are not recognized in earnings and generally do not impact PPE, net.
	Note 7 contains more information regarding the Partnership’s PPE.
Goodwill [Policy Text Block]	Goodwill and Intangible Assets
	Goodwill represents the excess of the cost of an acquisition over the fair value of the net identifiable assets acquired and liabilities assumed. Goodwill is tested for impairment at the reporting unit level at least annually, as of November 30, or more frequently when events occur and circumstances change that would more likely than not reduce the fair value of a reporting unit below its carrying amount. Accounting requirements provide that a reporting entity may perform an optional qualitative assessment on an annual basis to determine whether events occurred or circumstances changed that would more likely than not reduce the fair value of a reporting unit below its carrying amount. If an initial qualitative assessment identifies that it is more likely than not that the fair value of a reporting unit is less than its carrying amount, or the optional qualitative assessment is not performed, a quantitative analysis is performed under a two-step impairment test to measure whether the fair value of the reporting unit is less than its carrying amount. If based upon a quantitative analysis the fair value of the reporting unit is less than its carrying amount, including goodwill, the Partnership performs an analysis of the fair value of all the assets and liabilities of the reporting unit. If the implied fair value of the reporting unit's goodwill is determined to be less than its carrying amount, an impairment loss is recognized for the difference.
	Intangible assets are those assets which provide future economic benefit but have no physical substance. The Partnership recorded intangible assets for customer relationships obtained through its acquisitions. The customer relationships, which are included in Other Assets on the Consolidated Balance Sheets, have a finite life and are being amortized in a systematic and rational manner over their estimated useful lives.
	Note 8 contains additional information regarding the Partnership's goodwill and intangible assets.
Impairment or Disposal of Long-Lived Assets, Policy [Policy Text Block]	Impairment of Long-lived Assets (including Tangible and Definite-lived Intangible Assets)
	The Partnership evaluates its long-lived and intangible assets for impairment when, in management’s judgment, events or changes in circumstances indicate that the carrying amount of such assets may not be recoverable. When such a determination has been made, management’s estimate of undiscounted future cash flows attributable to the remaining economic useful life of the asset is compared to the carrying amount of the asset to determine whether an impairment has occurred. If an impairment of the carrying amount has occurred, the amount of impairment recognized in the financial statements is determined by estimating the fair value of the assets and recording a loss to the extent that the carrying amount exceeds the estimated fair value.
Interest Expense, Policy [Policy Text Block]	Capitalized Interest and Allowance for Funds Used During Construction (AFUDC)
	The Partnership records capitalized interest, which represents the cost of borrowed funds used to finance construction activities for operations where regulatory accounting is not applicable. The Partnership records AFUDC, which represents the cost of funds, including equity funds, applicable to regulated natural gas transmission plant under construction as permitted by FERC regulatory practices, in connection with the Partnership’s operations where regulatory accounting is applicable. Capitalized interest and the allowance for borrowed funds used during construction are recognized as a reduction to Interest expense and the allowance for equity funds used during construction is included in Miscellaneous other income, net within the Consolidated Statements of Income. The following table summarizes capitalized interest and the allowance for borrowed funds and allowance for equity funds used during construction (in millions):
		For the Year Ended
		December 31,
		2014		2013		2012
	Capitalized interest and allowance for borrowed funds used during construction	$	6.8	$	6.4	$	4.7
	Allowance for equity funds used during construction	0.5		0.2		0.4
Income Tax, Policy [Policy Text Block]	Income Taxes
	The Partnership is not a taxable entity for federal income tax purposes.  As such, it does not directly pay federal income tax. The Partnership’s taxable income or loss, which may vary substantially from the net income or loss reported in the Consolidated Statements of Income, is includable in the federal income tax returns of each partner. The aggregate difference in the basis of the Partnership’s net assets for financial and income tax purposes cannot be readily determined as the Partnership does not have access to the information about each partner’s tax attributes related to the Partnership. The subsidiaries of the Partnership directly incur some income-based state taxes which are presented in Income taxes on the Consolidated Statements of Income.
	Note 14 contains more information regarding the Partnership’s income taxes.
Revenue Recognition, Policy [Policy Text Block]	Revenue Recognition
	The maximum rates that may be charged by the majority of the Partnership's operating subsidiaries for their services are established through FERC’s cost-based rate-making process; however, rates charged by those operating subsidiaries may be less than those allowed by FERC. Revenues from transportation and storage services are recognized in the period the service is provided based on contractual terms and the related volumes transported or stored. In connection with some PAL and interruptible storage service agreements, cash is received at inception of the service period resulting in the recording of deferred revenues which are recognized in revenues over the period the services are provided. At December 31, 2014 and 2013, the Partnership had deferred revenues of $1.0 million and $7.9 million related to PAL and interruptible storage services and $6.2 million and $4.6 million related to a firm transportation agreement that was paid in advance. At December 31, 2014, the Partnership had deferred revenues of $2.5 million related to a brine supply contract for which certain future minimum volumes will need to be supplied by the Partnership. The deferred revenues related to PAL and interruptible storage services will be recognized through 2017 and the deferred revenues related to the firm transportation agreement will be recognized through 2018.
	Retained fuel is recognized in revenues at market prices in the month of retention for operations where regulatory accounting is not applicable. The related fuel consumed in providing transportation services is recorded in Fuel and transportation expenses at market prices in the month consumed. In some cases, customers may elect to pay cash for the cost of fuel used in providing transportation services instead of having fuel retained in-kind. Retained fuel included in Transportation on the Consolidated Statements of Income for the years ended December 31, 2014, 2013 and 2012 was $90.3 million, $76.9 million and $71.8 million.
	The Partnership has contractual retainage provisions in some of its ethylene storage contracts that provide for the Partnership to retain ownership of 0.5% of customer inventory volumes injected into storage wells. The Partnership may sell the retainage volumes if commercially marketable volumes are on hand. The Partnership recognizes revenue for ethylene retainage volumes upon the physical sale of such volumes.
	Under FERC regulations, certain revenues that the operating subsidiaries collect may be subject to possible refunds to customers. Accordingly, during a rate case, estimated refund liabilities are recorded considering regulatory proceedings, advice of counsel and estimated risk-adjusted total exposure, as well as other factors. At December 31, 2014 and 2013, there were no liabilities for any open rate case recorded on the Consolidated Balance Sheets.
Asset Retirement Obligations, Policy [Policy Text Block]	Asset Retirement Obligations
	The accounting requirements for existing legal obligations associated with the future retirement of long-lived assets require entities to record the fair value of a liability for an asset retirement obligation in the period during which the liability is incurred. The liability is initially recognized at fair value and is increased with the passage of time as accretion expense is recorded, until the liability is ultimately settled. The accretion expense is included within Operation and maintenance costs within the Consolidated Statements of Income. An amount corresponding to the amount of the initial liability is capitalized as part of the carrying amount of the related long-lived asset and depreciated over the useful life of that asset.
	Note 9 contains more information regarding the Partnership’s asset retirement obligations.
Environmental Costs, Policy [Policy Text Block]	Environmental Liabilities
	The Partnership records environmental liabilities based on management’s estimate of the undiscounted future obligation for probable costs associated with environmental assessment and remediation of operating sites. These estimates are based on evaluations and discussions with counsel and operating personnel and the current facts and circumstances related to these environmental matters.
	Note 5 contains more information regarding the Partnership’s environmental liabilities.
Pension and Other Postretirement Plans, Policy [Policy Text Block]	Defined Benefit Plans
	The Partnership maintains certain postretirement benefit plans for certain employees. The Partnership funds these plans through periodic contributions which are invested until the benefits are paid out to the participants. The net benefit cost of the plan is recorded in the Consolidated Statements of Income. The Partnership records an asset or liability based on the overfunded or underfunded status of the plan. Any deferred amounts related to unrecognized gains and losses or changes in actuarial assumptions are recorded as either a regulatory asset or liability or recorded as a component of accumulated other comprehensive income (AOCI) until those gains or losses are recognized in the Consolidated Statements of Income.
	Note 12 contains more information regarding the Partnership’s pension and postretirement benefit obligations.
Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block]	Unit-Based and Other Long-Term Compensation
	The Partnership provides awards of phantom common units (Phantom Common Units) to certain employees under its Long-Term Incentive Plan (LTIP). The Partnership also provides to certain employees awards of unit appreciation rights (UARs) and long-term cash bonuses (Long-Term Cash Bonuses) under the Boardwalk Pipeline Partners Unit Appreciation Rights and Cash Bonus Plan. In 2014, the Partnership entered into retention payment agreements with certain key employees.
	The Partnership measures the cost of an award issued in exchange for employee services based on the grant-date fair value of the award, or the stated amount in the case of the Long-Term Cash Bonuses and amounts under retention payment agreements. All outstanding awards are either required or expected to be settled in cash and are classified as a liability until settlement. The unit-based compensation awards are remeasured each reporting period until the final amount of awards is determined. The related compensation expense, less applicable estimates of forfeitures, is recognized over the period that employees are required to provide services in exchange for the awards, usually the vesting period.
	Note 12 contains additional information regarding the Partnership’s unit-based and other long-term compensation.
Partner Capital Accounts [Policy Text Block]	Partner Capital Accounts
	For purposes of maintaining capital accounts, items of income and loss of the Partnership are allocated among the partners each year, or portion thereof, in accordance with the partnership agreement. Generally, net income for each period is allocated among the partners based on their respective ownership interests after deducting any priority allocations in the form of cash distributions paid to the general partner as the holder of IDRs.
Derivatives, Policy [Policy Text Block]	Derivative Financial Instruments
	The Partnership uses futures, swaps, and option contracts (collectively, derivatives) to hedge exposure to various risks, including natural gas commodity and interest rate risk. The effective portion of the related unrealized gains and losses resulting from changes in fair values of the derivatives contracts designated as cash flow hedges are deferred as a component of AOCI. The deferred gains and losses are recognized in earnings when the hedged anticipated transactions affect earnings. Changes in fair value of derivatives that are not designated as cash flow hedges are recognized in earnings in the periods that those changes in fair value occur.
	The changes in fair values of the derivatives designated as cash flow hedges are expected to, and do, have a high correlation to changes in value of the anticipated transactions. Each reporting period the Partnership measures the effectiveness of the cash flow hedge contracts. To the extent the changes in the fair values of the hedge contracts do not effectively offset the changes in the estimated cash flows of the anticipated transactions, the ineffective portion of the hedge contracts is currently recognized in earnings. If it becomes probable that the anticipated transactions will not occur, hedge accounting would be terminated and changes in the fair values of the associated derivative financial instruments would be recognized currently in earnings. The Partnership discontinued an immaterial amount of cash flow hedges in 2014 and did not discontinue any cash flow hedges during 2013.
	The effective component of gains and losses resulting from changes in fair values of the derivatives designated as cash flow hedges are deferred as a component of AOCI. The deferred gains and losses associated with the anticipated operational sale of gas reported as current Gas stored underground are recognized in operating revenues when the anticipated transactions affect earnings. In situations where continued reporting of a loss in AOCI would result in recognition of a future loss on the combination of the derivative and the hedged transaction, the loss is required to be immediately recognized in earnings for the amount that is not expected to be recovered. No such losses were recognized in the years ended December 31, 2014, 2013, and 2012.
	Note 6 contains more information regarding the Partnership’s derivative financial instruments.

Accounting_Policies_Tables

Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2014
Accounting Policies [Abstract]
Summary of Capitalized Interest and Allowance for borrowed Funds	The following table summarizes capitalized interest and the allowance for borrowed funds and allowance for equity funds used during construction (in millions):
		For the Year Ended
		December 31,
		2014		2013		2012
	Capitalized interest and allowance for borrowed funds used during construction	$	6.8	$	6.4	$	4.7
	Allowance for equity funds used during construction	0.5		0.2		0.4

Acquisition_of_Boardwalk_Petro1

Acquisition of Boardwalk Petrochemical (Tables)	12 Months Ended
	Dec. 31, 2014
Business Combinations [Abstract]
Schedule of Business Acquisitions, by Acquisition [Table Text Block]	The acquisition of Evangeline was accounted for as a business combination using the acquisition method of accounting. The estimated fair values of the assets acquired and liabilities assumed related to the acquisition were as follows (in millions):
		Evangeline Acquisition Date
		Fair Value (3)
	Plant, property and equipment	$	253.3
	Customer-based intangibles (1)	20
	Goodwill (2)	21.9
	Total assets acquired	295.2
	Current liabilities	(0.3		)
	Noncurrent liabilities	(0.2		)
	Total liabilities assumed	(0.5		)
	Net assets acquired	$	294.7
	-1	Customer-based intangibles are estimated to have a weighted-average useful life of 30 years.
	-2	Goodwill represents the excess of the purchase price over the estimated fair value of the assets acquired, net of the fair value of the liabilities assumed in the acquisition.
	-3	The purchase price allocation is preliminary and is subject to change based on the final working capital adjustments which are expected to be settled in the first quarter 2015. For the period from October 8, 2014 to December 31, 2014, Evangeline contributed $0.7 million to the Partnership’s revenues and decreased the Partnership's net income by $1.8 million, excluding acquisition costs. The Partnership incurred $2.6 million of costs related to the acquisition of Boardwalk Petrochemical, which were expensed as incurred and were recorded in Administrative and general expenses. Pro forma data is not provided because the impact of the acquisition on the Partnership’s revenues and net income was not material.

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2014
Commitments and Contingencies Disclosure [Abstract]
Operating Leases of Lessee Disclosure [Table Text Block]	Lease Commitments
	The Partnership has various operating lease commitments extending through the year 2024 generally covering office space and equipment rentals. Total lease expense for the years ended December 31, 2014, 2013 and 2012 was approximately $10.7 million, $8.6 million and $6.4 million. The following table summarizes minimum future commitments related to these items at December 31, 2014 (in millions):
	2015	$	4.7
	2016	4.4
	2017	3.9
	2018	3.3
	2019	2.9
	Thereafter	13.6
	Total	$	32.8
Pipeline Capacity Agreements [Table Text Block]	Pipeline Capacity Agreements
	The Partnership’s operating subsidiaries have entered into pipeline capacity agreements with third-party pipelines that allow the operating subsidiaries to transport gas to off-system markets on behalf of customers. The Partnership incurred expenses of $10.1 million, $9.8 million and $9.1 million related to pipeline capacity agreements for the years ended December 31, 2014, 2013 and 2012. The future commitments related to pipeline capacity agreements as of December 31, 2014, were (in millions):
	2015	$	6.9
	2016	6.3
	2017	6.2
	2018	2
	2019	—
	Thereafter	—
	Total	$	21.4
Capital Lease [Table Text Block]	Capital Lease
	The Partnership entered into an agreement to lease an office building in Owensboro, Kentucky. The construction of the building was completed and the Partnership took possession of the building in the third quarter 2013, at which time the Partnership recorded a capital lease asset and obligation of $10.5 million. The office building lease has a term of fifteen years with two twenty-year renewal options. Future commitments under this capital lease are as follows (in millions):
	2015	$	1
	2016	1
	2017	1
	2018	1
	2019	1.1
	Thereafter	9.5
	Total minimum lease payments	14.6
	Less amounts representing interest	(4.6		)
	Present value of obligation under capital lease	10
	Less: current portion of obligations under capital lease	(0.4		)
	(recorded in Other current liabilities)
	Long-term obligations under capital lease	$	9.6
	Amortization of the office building under the capital lease for the year ended December 31, 2014 and 2013 was $0.7 million and $0.3 million and was included in Depreciation and amortization. As of December 31, 2014 and 2013, assets recorded in Natural gas transmission and other plant under the capital lease were $10.5 million and the accumulated amortization was $1.0 million and $0.3 million.

Fair_Value_Measurements_Deriva1

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI) Accumulated Other Comprehensive Income (Loss) Net of Tax (Tables)	12 Months Ended
	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss), Net of Tax [Abstract]
Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block]	The following table shows the components and reclassifications to net income of Accumulated other comprehensive loss which is included in Partners' Capital on the Consolidated Balance Sheets for the years ended December 31, 2012 through 2014 (in millions):
		Cash Flow Hedges			Pension and Other Postretirement Benefit Costs			Total
	Beginning balance, January 1, 2012	$	(10.4	)	$	(39.0	)	$	(49.4	)
	Loss recorded in accumulated other comprehensive loss	(7.1		)	—			(7.1		)
	Reclassifications:
	Other operating revenues	(0.1		)	—			(0.1		)
	Interest expense (1)	2.1			—			2.1
	Pension and other postretirement benefit costs	—			(12.8		)	(12.8		)
	Ending balance, December 31, 2012	$	(15.5	)	$	(51.8	)	$	(67.3	)
	Gain recorded in accumulated other comprehensive loss	1.6			—			1.6
	Reclassifications:
	Transportation operating revenues	0.1			—			0.1
	Other operating revenues	(0.1		)	—			(0.1		)
	Disposal of operating assets	(1.2		)	—			(1.2		)
	Interest expense (1)	2.4			—			2.4
	Pension and other postretirement benefit costs	—			0.7			0.7
	Ending balance, December 31, 2013	$	(12.7	)	$	(51.1	)	$	(63.8	)
	Loss recorded in accumulated other comprehensive loss	(0.7		)	—			(0.7		)
	Reclassifications:
	Other operating revenues	0.2			—			0.2
	Interest expense (1)	2.4			—			2.4
	Pension and other postretirement benefit costs	—			(10.9		)	(10.9		)
	Ending balance, December 31, 2014	$	(10.8	)	$	(62.0	)	$	(72.8	)
	-1	Related to amounts deferred in AOCI from Treasury rate locks described above.

Fair_Value_Measurements_Deriva2

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI) Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Fair Value, by Balance Sheet Grouping [Table Text Block]	The carrying amount and estimated fair values of the Partnership's financial assets and liabilities which were not recorded at fair value on the Consolidated Balance Sheets as of December 31, 2014, and 2013, were as follows (in millions):
	As of December 31, 2014				Estimated Fair Value
	Financial Assets	Carrying Amount			Level 1		Level 2		Level 3		Total
	Cash and cash equivalents	$	6.6		$	6.6	$	—	$	—	$	6.6
	Financial Liabilities
	Long-term debt	$	3,680.10	(1)	$	—	$	3,787.40	$	—	$	3,787.40
	(1) The carrying amount of long-term debt excludes a $9.6 million long-term capital lease obligation.
	As of December 31, 2013				Estimated Fair Value
	Financial Assets	Carrying Amount			Level 1		Level 2		Level 3		Total
	Cash and cash equivalents	$	28.5		$	28.5	$	—	$	—	$	28.5
	Financial Liabilities
	Long-term debt	$	3,414.40	(1)	$	—	$	3,573.80	$	—	$	3,573.80
	(1) The carrying amount of long-term debt excludes a $10.0 million long-term capital lease obligation.

Property_Plant_and_Equipment_P1

Property, Plant and Equipment (PPE) (Tables)	12 Months Ended
	Dec. 31, 2014
Property, Plant and Equipment [Abstract]
Property, Plant and Equipment [Table Text Block]	The following table presents the Partnership’s PPE as of December 31, 2014 and 2013 (in millions):
	Category		2014			Weighted-Average	2013			Weighted-Average
			Amount			Useful Lives	Amount			Useful Lives
						(Years)				(Years)
	Depreciable plant:
	Transmission		$	7,719.80		37	$	7,067.70		37
	Storage		758.5			38	749.7			38
	Gathering		336.7			27	326			27
	General		170			14	160.3			13
	Rights of way and other		114.9			36	111.1			35
	Total utility depreciable plant		9,099.90			37	8,414.80			36
	Non-depreciable:
	Construction work in progress		105.5				174.5
	Storage		105.5				90.8
	Land		28.4				26.9
	Other		16.3				16.3
	Total non-depreciable assets		255.7				308.5
	Total PPE		9,355.60				8,723.30
	Less:  accumulated depreciation		1,766.40				1,489.20
	Total PPE, net		$	7,589.20			$	7,234.10
	The non-depreciable assets were not included in the calculation of the weighted-average useful lives.
Gross PPE Investments and Related Accumulated Depreciation	The following table presents the gross PPE investment and related accumulated depreciation for the Partnership’s undivided interests as of December 31, 2014 and 2013 (in millions):
		2014						2013
		Gross PPE			Accumulated Depreciation			Gross PPE			Accumulated Depreciation
		Investment						Investment
	Bistineau storage	$	64.3		$	17.5		$	55.8		$	15.1
	Mobile Bay Pipeline	13			3.6			11.1			3.1
	NGL pipelines and facilities	34.8			2.2			34.8			1.3
	Offshore and other assets	18.8			13.7			19			13.4
	Total	$	130.9		$	37		$	120.7		$	32.9

Goodwill_and_Intangible_Assets1

Goodwill and Intangible Assets (Tables)	12 Months Ended
	Dec. 31, 2014
Goodwill and Intangible Assets Disclosure [Abstract]
Schedule of Goodwill [Table Text Block]	Changes in the gross amounts of goodwill for the Partnership are summarized as follows (in millions):
	Balance as of January 1, 2013	$	267
	Goodwill impairment charge	(51.5		)
	Balance as of December 31, 2013	215.5
	Acquisition of Boardwalk Petrochemical (1)	21.9
	Balance as of December 31, 2014	$	237.4
	(1) Refer to Note 4 for further information on the acquisition of Boardwalk Petrochemical.
Schedule of Finite-Lived Intangible Assets [Table Text Block]	The following table contains information regarding the Partnership's intangible assets, which includes customer relationships acquired as part of its acquisitions (in millions):
		December 31,
		2014			2013
	Gross carrying amount	$	59.4		$	39.4
	Accumulated amortization	(3.5		)	(2.1		)
	Net carrying amount	$	55.9		$	37.3
Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block]	For the year ended December 31, 2014, 2013 and 2012 amortization expense for intangible assets totaled $1.4 million, $1.3 million and $0.8 million and was recorded in Depreciation and amortization on the Consolidated Statements of Income. Amortization expense for the next five years and in total thereafter as of December 31, 2014, is expected to be as follows (in millions):
	2015	$	2
	2016	2
	2017	2
	2018	2
	2019	2
	Thereafter	45.9
		$	55.9

Asset_Retirement_Obligations_A1

Asset Retirement Obligations (ARO) (Tables)	12 Months Ended
	Dec. 31, 2014
Asset Retirement Obligation Disclosure [Abstract]
Asset Retirement Obligation	The following table summarizes the aggregate carrying amount of the Partnership’s ARO (in millions):
		2014			2013
	Balance at beginning of year	$	47.1		$	39
	Liabilities recorded	4.3			8
	Liabilities settled	(6.9		)	(1.7		)
	Accretion expense	1.8			1.8
	Balance at end of year	46.3			47.1
	Less:  Current portion of asset retirement obligations	(6.4		)	(7.8		)
	Long-term asset retirement obligations	$	39.9		$	39.3

Regulatory_Assets_and_Liabilit1

Regulatory Assets and Liabilities (Tables)	12 Months Ended
	Dec. 31, 2014
Regulatory Assets and Liabilities Disclosure [Abstract]
Schedule of Regulatory Assets and Liabilities	The amounts recorded as regulatory assets and liabilities in the Consolidated Balance Sheets as of December 31, 2014 and 2013, are summarized in the table below. The table also includes amounts related to unamortized debt expense and unamortized discount on long-term debt. While these amounts are not regulatory assets and liabilities, they are a critical component of the embedded cost of debt financing utilized in the Texas Gas rate proceedings. The tax effect of the equity component of AFUDC represents amounts recoverable from rate payers for the tax recorded in regulatory accounting. Certain amounts in the table are reflected as a negative, or a reduction, to be consistent with the regulatory books of account. The period of recovery for the regulatory assets included in rates varies from one to eighteen years. The remaining period of recovery for regulatory assets not yet included in rates would be determined in future rate proceedings. None of the regulatory assets shown below were earning a return as of December 31, 2014 and 2013 (in millions):
		2014			2013
	Regulatory Assets:
	Pension	$	10.6		$	10.6
	Tax effect of AFUDC equity	3.5			3.9
	Unamortized debt expense and premium on reacquired debt	9.6			11.5
	Fuel tracker	0.2			0.8
	Total regulatory assets	$	23.9		$	26.8
	Regulatory Liabilities:
	Cashout and fuel tracker	$	0.9		$	1.1
	Provision for other asset retirement	60.5			57.6
	Unamortized discount on long-term debt	(1.5		)	(1.8		)
	Postretirement benefits other than pension	34.2			32.7
	Total regulatory liabilities	$	94.1		$	89.6

Financing_Tables

Financing (Tables)	12 Months Ended
	Dec. 31, 2014
Debt Disclosure [Abstract]
Schedule of Long-term Debt Instruments [Table Text Block]	The following table presents all long-term debt issues outstanding as of December 31, 2014 and 2013 (in millions):
		2014				2013
	Notes and Debentures:
	Boardwalk Pipelines
	5.88% Notes due 2016	$	250			$	250
	5.50% Notes due 2017	300				300
	5.20% Notes due 2018	185				185
	5.75% Notes due 2019	350				350
	3.375% Notes due 2023	300				300
	4.95% Notes due 2024 (Boardwalk Pipelines 2024 Notes)	350				—
	Gulf South
	5.05% Notes due 2015 (Gulf South 2015 Notes)	275				275
	6.30% Notes due 2017	275				275
	4.00% Notes due 2022	300				300
	Texas Gas
	4.60% Notes due 2015 (Texas Gas 2015 Notes)	250				250
	4.50% Notes due 2021	440				440
	7.25% Debentures due 2027	100				100
	Total notes and debentures	3,375.00				3,025.00
	Term Loan	200				225
	Revolving Credit Facility:
	Gulf Crossing	120				175
	Capital lease obligation	9.6				10
		3,704.60				3,435.00
	Less: unamortized debt discount	(14.9		)		(10.6		)
	Total Long-Term Debt and Capital Lease Obligation	$	3,689.70			$	3,424.40
Schedule of Maturities of Long-term Debt [Table Text Block]	Maturities of the Partnership’s long-term debt for the next five years and in total thereafter are as follows (in millions):
	2015	$	525
	2016	250
	2017	895
	2018	185
	2019	350
	Thereafter	1,490.00
	Total long-term debt	$	3,695.00
Debt Issuances	For the years ended December 31, 2014, 2013 and 2012, the Partnership completed the following debt issuances (in millions, except interest rates):
	Date of		Issuing Subsidiary		Amount of				Purchaser			Net			Interest		Maturity Date	Interest Payable
	Issuance				Issuance				Discounts			Proceeds			Rate
									and
									Expenses
	Nov-14		Boardwalk Pipelines		$	350			$	7.1		$	342.9	(1)	4.95	%	December 15, 2024	June 15 and December 15
	Nov-12		Boardwalk Pipelines		$	300			$	2.4		$	297.6	(2)	3.375	%	February 1, 2023	February 1 and August 1
	Jun-12		Gulf South		$	300			$	3.5		$	296.5	(3)	4	%	June 15, 2022	June 15 and December 15
	-1	The net proceeds of this offering were used to retire all of the outstanding Gulf South 2015 Notes and the remainder of the net proceeds was used to reduce outstanding borrowings under the Partnership’s revolving credit facility.
	-2	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and repay all amounts outstanding under the subordinated loan agreement that was in place at that time, or $100.0 million.
	-3	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and to redeem $225.0 million of Gulf South's 5.75% notes due August 2012 (2012 Notes) discussed below. BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.
Equity Issuance	For the years ended December 31, 2014, 2013 and 2012, the Partnership completed the following issuances and sales of common units (in millions, except the issuance price):
	Month of Offering		Number of		Issuance		Less Underwriting Discounts and Expenses		Net Proceeds		Common Units Outstanding	Common Units Held by the Public
			Common Units		Price				(including General Partner Contribution)		After Offering	After Offering
	May-13		12.7		$30.12		$12.30		$376.50		220.3	117.6
	Oct-12	(1)	11.2		$26.99		$10.40		$297.60		207.7	105
	Aug-12	(1)	11.6		$27.80		$11.20		$317.90		196.5	93.8
	Feb-12	(1)	9.2		$27.55		$8.50		$250.20		184.9	82.2
	-1	BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.
Summary of Changes in Partnership Capital	The following table summarizes changes in the Partnership’s common and class B units since January 1, 2012 (in millions):
		Common			Class B
		Units			Units(1)
	Balance, January 1, 2012	175.7			22.9
	Common units issued in connection with underwritten offerings	32			—
	Balance, December 31, 2012	207.7			22.9
	Common units issued in connection with underwritten offerings	12.7			—
	Conversion of class B units	22.9			(22.9	)
	Balance, December 31, 2013 and 2014	243.3			—
	-1	On October 9, 2013, all of the 22.9 million class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.

Employee_Benefits_Tables

Employee Benefits (Tables)	12 Months Ended
	Dec. 31, 2014
Employee Benefits [Abstract]
Projected Benefit Obligation, Fair Value of Assets, Funded Status and the Amounts Not Yet Recognized As Components of Net Periodic Pension and Postretirement Benefits Cost [Table Text Block]	Projected Benefit Obligation, Fair Value of Assets and Funded Status
	The projected benefit obligation, fair value of assets, funded status and the amounts not yet recognized as components of net periodic pension and postretirement benefits cost for the Retirement Plans and PBOP at December 31, 2014 and 2013, were as follows (in millions):
		Retirement Plans								PBOP
		For the Year Ended								For the Year Ended
		December 31,								December 31,
		2014				2013				2014				2013
	Change in benefit obligation:
	Benefit obligation at beginning of period	$	148.5			$	152.5			$	50			$	59.5
	Service cost	3.9				3.9				0.4				0.5
	Interest cost	5.8				5				2.2				2.1
	Plan participants’ contributions	—				—				0.9				0.8
	Actuarial loss (gain)	3.6				(1.2		)		5.2				(8.3		)
	Benefits paid	(0.5		)		(0.4		)		(3.6		)		(4.6		)
	Settlement	(11.4		)		(11.3		)		—				—
	Benefit obligation at end of period	$	149.9			$	148.5			$	55.1			$	50
	Change in plan assets:
	Fair value of plan assets at beginning of period	$	131.4			$	125.7			$	80.8			$	86.7
	Actual return on plan assets	8.2				14.4				9.1				(2.2		)
	Benefits paid	(0.5		)		(0.4		)		(3.6		)		(4.6		)
	Settlement	(11.4		)		(11.3		)		—				—
	Company contributions	3				3				0.1				0.1
	Plan participants’ contributions	—				—				0.9				0.8
	Fair value of plan assets at end of period	$	130.7			$	131.4			$	87.3			$	80.8
	Funded status	$	(19.2	)		$	(17.1	)		$	32.2			$	30.8
	Items not recognized as components of net periodic cost:
	Prior service cost (credit)	$	—			$	—			$	(8.6	)		$	(16.4	)
	Net actuarial loss	26				24.4				10.7				10.6
	Total	$	26			$	24.4			$	2.1			$	(5.8	)
Schedule of Accumulated Benefit Obligations in Excess of Fair Value of Plan Assets [Table Text Block]	At December 31, 2014 and 2013, the following aggregate information relates only to the underfunded plans (in millions):
		Retirement Plans
		For the Year Ended
		December 31,
		2014				2013
	Projected benefit obligation	$	149.9			$	148.5
	Accumulated benefit obligation	139.7				138.4
	Fair value of plan assets	130.7				131.4
Schedule of Net Benefit Costs [Table Text Block]	Components of Net Periodic Benefit Cost
	Components of net periodic benefit cost for both the Retirement Plans and PBOP for the years ended December 31, 2014, 2013 and 2012 were as follows (in millions):
		Retirement Plans												PBOP
		For the Year Ended												For the Year Ended
		December 31,												December 31,
		2014				2013				2012				2014				2013			2012
	Service cost	$	3.9			$	3.9			$	4			$	0.4			$	0.5		$	0.5
	Interest cost	5.8				5				5.8				2.2				2.1			2.4
	Expected return on plan assets	(9.5		)		(9.1		)		(8.6		)		(4.2		)		(4.5		)	(4.3		)
	Amortization of prior service credit	—				—				—				(7.8		)		(7.8		)	(7.8		)
	Amortization of unrecognized net loss	1.4				2.1				2.1				0.3				—			0.1
	Settlement charge	1.9				1.7				—				—				—			—
	Net periodic benefit cost	$	3.5			$	3.6			$	3.3			$	(9.1	)		$	(9.7	)	$	(9.1	)
Schedule of Expected Benefit Payments [Table Text Block]	Estimated Future Benefit Payments
	The following table shows benefit payments, which reflect expected future service, as appropriate, which are expected to be paid for both the Retirement Plans and PBOP (in millions):
		Retirement Plans				PBOP
	2015	$	16.3			$	3.1
	2016	15				3.1
	2017	14.8				3.2
	2018	15				3.3
	2019	15.7				3.3
	2020-2024	67.1				16.5
Weighted-Average Assumptions Used to Determine Benefit Obligations	Weighted –Average Assumptions
	Weighted-average assumptions used to determine benefit obligations for the years ended December 31, 2014 and 2013, were as follows:
		Retirement Plans												PBOP
		For the Year Ended												For the Year Ended
		December 31,												December 31,
		2014						2013						2014			2013
		Pension			SRP			Pension			SRP
	Discount rate	3.35	%		3.75	%		4	%		4.25	%		3.9	%		4.5	%
	Expected return on plan assets	7.5	%		7.5	%		7.5	%		7.5	%		5.3	%		5.3	%
	Rate of compensation increase	3.5	%		3.5	%		3.5	%		3.5	%		—	%		—	%
Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost	Weighted-average assumptions used to determine net periodic benefit cost for the periods indicated were as follows:
		Retirement Plans																	PBOP
		For the Year Ended																	For the Year Ended
		December 31,																	December 31,
		2014						2013					2012						2014		2013			2012
		Pension			SRP			Pension		SRP			Pension			SRP
	Discount rate	4	%		4.25	%		3.25%/4.10%	(1)	3.5	%		4.25	%		4.25	%		4.5	%	3.9	%		4.7	%
	Expected return on plan assets	7.5	%		7.5	%		7.50%		7.5	%		7.5	%		7.5	%		5.3	%	5.3	%		5.3	%
	Rate of compensation increase	3.5	%		3.5	%		3.50%		3.5	%		4	%		4	%		—	%	—	%		—	%
	(1) Pension expense was remeasured at September 30, 2013, to reflect a settlement.
Schedule of Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates [Table Text Block]	PBOP Assumed Health Care Cost Trends
	Assumed health care cost trend rates have a significant effect on the amounts reported for PBOP. A one-percentage-point change in assumed trend rates for health care costs would have had the following effects on amounts reported for the year ended December 31, 2014 (in millions):
	Effect of 1% Increase:		2014
	Benefit obligation at end of year		$	2.2
	Total of service and interest costs for year		0.1
	Effect of 1% Decrease:
	Benefit obligation at end of year		$	(1.9	)
	Total of service and interest costs for year		(0.1		)
Fair Values of Pension Plan Assets By Asset Class Master Trust [Table Text Block]	The following table sets forth by level within the fair value hierarchy a summary of the Master Trust’s investments measured at fair value on a recurring basis at December 31, 2014 (in  millions):
		Master Trust Assets
		Level 1				Level 2				Level 3				Total
	Equity securities	$	42.3			$	—			$	—			$	42.3
	Short-term investments	11.8				—				—				11.8
	Other assets	1.1				—				—				1.1
	Fixed income mutual funds	98.7				—				—				98.7
	Asset-backed securities	—				6				—				6
	Limited partnerships :
	Hedge funds	—				56.7				29.5				86.2
	Private equity	—				—				10.1				10.1
	Total investments	$	153.9			$	62.7			$	39.6			$	256.2
	The following table sets forth by level within the fair value hierarchy a summary of the Master Trust’s investments measured at fair value on a recurring basis at December 31, 2013 (in  millions):
		Master Trust Assets
		Level 1				Level 2				Level 3				Total
	Equity securities	$	44.6			$	—			$	—			$	44.6
	Short-term investments	4.4				—				—				4.4
	Other assets	—				3.4				—				3.4
	Fixed income mutual funds	100.1				0.3				—				100.4
	Asset-backed securities	—				5.8				—				5.8
	Limited partnerships:
	Hedge funds	—				57.5				29.7				87.2
	Private equity	—				—				11.7				11.7
	Total investments	$	149.1			$	67			$	41.4			$	257.5
Fair Value Measurement Using Significant Unobservable Inputs Master Trust [Table Text Block]	The following table presents a reconciliation of the beginning and ending balances of the fair value measurements using significant unobservable inputs (Level 3) for the Master Trust (in millions):
		Limited				Limited
		Partnerships:				Partnerships:
		Hedge Funds				Private Equity
	Balance, January 1, 2013	$	32			$	7.1
	Actual return on assets still held	6.2				2.1
	Actual return on assets sold	(0.3		)		(0.3		)
	Purchases, sales and settlements	(8.2		)		2.8
	Net transfers in/(out) of Level 3	—				—
	Balance, December 31, 2013	29.7				11.7
	Actual return on assets still held	2.1				0.2
	Actual return on assets sold	0.1				0.8
	Purchases, sales and settlements	(2.4		)		(2.6		)
	Net transfers in/(out) of Level 3	—				—
	Balance, December 31, 2014	$	29.5			$	10.1
Fair Values of Pension Plan Assets By Asset Class [Table Text Block]	The following table sets forth by level within the fair value hierarchy a summary of the PBOP trust investments measured at fair value on a recurring basis at December 31, 2014 (in  millions):
		PBOP Trust Assets
		Level 1				Level 2				Level 3				Total
	Short-term investments	$	3.2			$	—			$	—			$	3.2
	Fixed income mutual funds	3				—				—				3
	Asset-backed securities	—				20.4				—				20.4
	Corporate bonds	—				17.8				—				17.8
	Tax exempt securities	—				42.9				—				42.9
	Total investments	$	6.2			$	81.1			$	—			$	87.3
	The following table sets forth by level within the fair value hierarchy a summary of the PBOP trust investments measured at fair value on a recurring basis at December 31, 2013 (in  millions):
		PBOP Trust Assets
		Level 1				Level 2				Level 3				Total
	Short-term investments	$	2.7			$	—			$	—			$	2.7
	Fixed income mutual funds	2.8				—				—				2.8
	Asset-backed securities	—				19.8				—				19.8
	Corporate bonds	—				16.9				—				16.9
	Tax exempt securities	—				38.6				—				38.6
	Total investments	$	5.5			$	75.3			$	—			$	80.8
Disclosure of Share Based Compensation Arrangements by Share Based Payment Award LTIP [Table Text Block]	A summary of the status of the Phantom Common Units granted under the Partnership’s LTIP as of December 31, 2014 and 2013, and changes during the years ended December 31, 2014 and 2013, is presented below:
		Phantom Common Units			Total Fair Value				Weighted-Average Vesting Period
					(in millions)				(in years)
	Outstanding at January 1, 2013 (1)	192,595			$	4.7			2
	Granted	220,808			5.7				2.8
	Forfeited	(33,355	)		—				—
	Outstanding at December 31, 2013 (1)	380,048			10.9				1.5
	Paid	(171,411	)		(3.5		)		—
	Forfeited	(8,968	)		—				—
	Outstanding at December 31, 2014 (1)	199,669			$	4.1			0.9
	-1	Represents fair value and remaining weighted-average vesting period of outstanding awards at the end of the period.
Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block]	A summary of the outstanding UARs granted under the Partnership’s UAR and Cash Bonus Plan as of December 31, 2014 and 2013, and changes during 2014 and 2013 is presented below:
		UARs			Weighted- Average				Total Fair Value				Weighted-Average Vesting Period
					Exercise Price				(in millions)				(in years)
	Outstanding at January 1, 2013 (1)	605,747			$	29.18			$	1.7			1.4
	Paid	(359,148	)
	Forfeited	(61,400	)
	Granted (2)	293,809			27.57				1.8				2.8
	Outstanding at December 31, 2013 (1)	479,008			27.47				1.9				1.5
	Vested (3)	(203,168	)
	Forfeited	(10,348	)
	Outstanding at December 31, 2014 (1)	265,492			$	27.57			$	—			0.9
	-1	Represents weighted-average exercise price, remaining weighted-average vesting period and total fair value of outstanding awards at the end of the period.
	-2	Represents the weighted-average exercise price and weighted-average vesting period of awards at grant date. The exercise price for each UAR granted was set at $27.57, the closing price of the Partnership’s common units on the New York Stock Exchange on the grant date on February 7, 2013.
	-3	Units vested and expired with no value.
Valuation Assumptions Under Unit Appreciation Rights [Table Text Block]	The fair value of the UARs was based on the computed value of a call on the Partnership’s common units at the exercise price. The following assumptions were used as inputs to the Black-Scholes valuation model for grants made during 2013. No UARs were granted in 2014.
		Grant Date Assumptions for Grants Made in 2013
	Expected life (years)	2.8
	Risk free interest rate (1)	0.35%
	Expected volatility (2)	32%
	-1	Based on the U.S. Treasury yield curve corresponding to the remaining life of the UAR.
	-2	Based on the historical volatility of the Partnership’s common units.
Disclosure of Share Based Compensation Arrangements By Share Based Payment Award SLTIP [Table Text Block]	A summary of the status of the Partnership’s SLTIP as of December 31, 2014 and 2013, and changes during the years ended December 31, 2014 and 2013, is presented below:
		Phantom GP Units			Total Fair Value				Weighted-Average Vesting Period
					(in millions)				(in years)
	Outstanding at January 1, 2013 (1)	145			$	6.9			0.2
	Paid	(145	)		(7.2		)		—
	Outstanding at December 31, 2013 and 2014	—			$	—			—
	-1	Represents fair value and remaining weighted-average vesting period of outstanding awards at the end of the period.

Cash_Distributions_and_Net_Inc1

Cash Distributions and Net Income per Unit (Tables)	12 Months Ended
	Dec. 31, 2014
Partners' Capital Notes [Abstract]
Schedule of partnership quarterly distribution allocation	The Partnership’s cash distribution policy requires that the Partnership distribute to its various ownership interests on a quarterly basis all of its available cash, as defined in its partnership agreement. IDRs, which represent a limited partner ownership interest and are currently held by the Partnership’s general partner, represent the contractual right to receive an increasing percentage of quarterly distributions of available cash as follows:
		Total Quarterly Distribution		Marginal Percentage
				Interest in
				Distributions
		Target Amount		Limited Partner	General
				Unitholders (1)	Partner
					and IDRs
	First Target Distribution	up to $0.4025		98%	2%
	Second Target Distribution	above $0.4025 up to $0.4375		85%	15%
	Third Target Distribution	above $0.4375 up to $0.5250		75%	25%
	Thereafter	above $0.5250		50%	50%
	-1	The class B unitholders participated in distributions on a pari passu basis with the Partnership’s common units up to $0.30 per unit per quarter. The class B units did not participate in quarterly distributions above $0.30 per unit and converted into common units on a one-for-one basis on October 9, 2013.
Dividends Declared [Table Text Block]	The Partnership has declared quarterly distributions per unit to unitholders of record, including holders of common and class B units (through October 9, 2013) and the 2% general partner interest and IDRs held by its general partner as follows (in millions, except distribution per unit):
	Payment Date		Distribution			Amount Paid to Common			Amount Paid			Amount Paid to General Partner (Including IDRs) (1)
			per Unit			Unitholders			to Class B
									Unitholder
	November 20, 2014		$	0.1		$	24.3		$	—		$	0.5
	August 21, 2014		0.1			24.3			—			0.5
	May 15, 2014		0.1			24.3			—			0.5
	February 27, 2014		0.1			24.3			—			0.5
	November 14, 2013		0.5325			129.5			—		(2)	12.4
	August 15, 2013		0.5325			117.3			6.9			11.4
	May 16, 2013		0.5325			110.6			6.8			10.7
	February 28, 2013		0.5325			110.6			6.9			10.8
	November 15, 2012		0.5325			110.6			6.9			10.8
	August 16, 2012		0.5325			104.6			6.9			10.2
	May 17, 2012		0.5325			98.5			6.8			9.6
	February 23, 2012		0.53			98.1			6.8			9.1
	-1	In February 2014, the Partnership decreased its distribution rate to $0.10 per common unit. As a result of the reduced distribution rate, the quarterly target distribution levels for IDR payout were not met and the Partnership paid no amounts with respect to the IDRs in 2014. In 2013 and 2012, the Partnership paid $34.6 million and $30.1 million in distributions on behalf of IDRs.
	-2	On October 9, 2013, all of the 22.9 million Class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.
Distributions Made to Limited Partner, by Distribution [Table Text Block]	The following table provides a reconciliation of net income and the assumed allocation of net income to the common units for purposes of computing net income per unit for the year ended December 31, 2014, (in millions, except per unit data):
		Total			Common			General Partner and IDRs
					Units
	Net income	$	146.8
	Less: Net loss attributable to noncontrolling interests	(86.8		)
	Net income attributable to controlling interests	233.6
	Declared distribution	99.2			$	97.2		$	2
	Assumed allocation of undistributed net income	134.4			131.7			2.7
	Assumed allocation of net income attributable to limited	$	233.6		$	228.9		$	4.7
	partner unitholders and general partner
	Weighted-average units outstanding				243.3
	Net income per unit				$	0.94
	The following table provides a reconciliation of net income and the assumed allocation of net income to the common and class B units for purposes of computing net income per unit for the year ended December 31, 2013. Basic net income per unit is calculated based on the weighted average number of units outstanding for the period. Diluted net income per unit is calculated assuming that the class B units converted on the date that they became convertible, or July 1, 2013 (in millions, except per unit data):
		Total			Common			Class B			General Partner and IDRs
					Units			Units
	Net income	$	250.2
	Less: Net loss attributable to noncontrolling interests	(3.5		)
	Net income attributable to controlling interests	253.7
	Declared distribution	430.5			$	381.8		$	13.7		$	35
	Assumed allocation of undistributed net loss (basic)	(176.8		)	(160.5		)	(12.8		)	(3.5		)
	Assumed allocation of net income attributable to limited	253.7			221.3			0.9			31.5
	partner unitholders and general partner — basic
	Allocation for diluted earnings per unit	—			(4.6		)	4.6			—
	Assumed allocation of net income attributable to limited	$	253.7		$	216.7		$	5.5		$	31.5
	partner unitholders and general partner — diluted
	Weighted-average units outstanding — basic				220.5			17.6
	Weighted-average units outstanding — diluted				226.8			11.3
	Net income per unit — basic				$	1		$	0.05
	Net income per unit — diluted				$	0.96		$	0.48
	The following table provides a reconciliation of net income and the assumed allocation of net income to the common and class B units for purposes of computing net income per unit for the year ended December 31, 2012 (in millions, except per unit data):
		Total			Common			Class B			General Partner and IDRs
					Units			Units
	Net income	$	306
	Less: Net loss attributable to predecessor equity	(2.2		)
	Net income attributable to limited partner unitholders and	308.2
	general partner
	Declared distribution	493.1			$	424.3		$	27.5		$	41.3
	Assumed allocation of undistributed net loss	(184.9		)	(162.0		)	(19.2		)	(3.7		)
	Assumed allocation of net income attributable to limited	$	308.2		$	262.3		$	8.3		$	37.6
	partner unitholders and general partner
	Weighted-average units outstanding				191.9			22.9
	Net income per unit				$	1.37		$	0.36

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Schedule of Components of Income Tax Expense (Benefit) [Table Text Block]	Following is a summary of the provision for income taxes for the periods ended December 31, 2014, 2013 and 2012 (in millions):
		For the Year Ended December 31,
		2014		2013		2012
	Current expense:
	State	$	0.3	$	0.4	$	(0.2	)
	Total	0.3		0.4		(0.2		)
	Deferred provision:
	State	0.1		0.1		0.7
	Total	0.1		0.1		0.7
	Income taxes	$	0.4	$	0.5	$	0.5

Credit_Risk_Tables

Credit Risk (Tables)	12 Months Ended
	Dec. 31, 2014
Risks and Uncertainties [Abstract]
Operating revenues received from the partnership's major customer and percentage of total operating revenues earned	Operating revenues received from the Partnership’s major customer (in millions) and the percentage of total operating revenues earned from that customer were:
		For the Year Ended December 31,
		2014			2013			2012
		Revenue		%	Revenue		%	Revenue		%
	Devon Gas Services, LP	$	120.5	10%	$	127.1	11%	$	133.3	12%

Supplemental_Disclosure_of_Cas1

Supplemental Disclosure of Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2014
Supplemental Cash Flow Elements [Abstract]
Schedule of Cash Flow, Supplemental Disclosures [Table Text Block]	Supplemental Disclosure of Cash Flow Information (in millions):
		For the Year Ended December 31,
		2014		2013		2012
	Cash paid during the period for:
	Interest (net of amount capitalized) (1)	$	153	$	151	$	169.8
	Income taxes, net	0.1		0.3		0.2
	Non-cash adjustments:
	Accounts payable and PPE	36.9		38.1		37.9
	Capital lease obligations incurred	—		10.5		—
	-1	The 2012 period includes payments of $9.6 million related to the settlements of interest rate derivatives.

Selected_Quarterly_Financial_D1

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2014
Quarterly Financial Data [Abstract]
Schedule of Quarterly Financial Information [Table Text Block]	The following tables summarize selected quarterly financial data for 2014 and 2013 for the Partnership (in millions, except for earnings per unit):
		2014
		For the Quarter Ended:
		31-Dec			30-Sep			30-Jun			31-Mar
	Operating revenues	$	304.6		$	278.9		$	293.4		$	356.9
	Operating expenses	224.1			210.4			196.9			204.3
	Operating income	80.5			68.5			96.5			152.6
	Interest expense, net	44.2			39.9			40			40.8
	Other (income) expense	(0.6		)	0.1			0.5			86
	Income before income taxes	36.9			28.5			56			25.8
	Income taxes	—			0.1			0.1			0.2
	Net income	36.9			28.4			55.9			25.6
	Net earnings (loss) attributable to	0.1			(0.8		)	(1.5		)	(84.6		)
	noncontrolling interests
	Net income attributable to	$	36.8		$	29.2		$	57.4		$	110.2
	controlling interests
	Net income per unit:	$	0.15		$	0.12		$	0.23		$	0.44
		2013
		For the Quarter Ended:
		31-Dec			30-Sep			30-Jun			31-Mar
	Operating revenues	$	312.9		$	275.5		$	288.7		$	328.5
	Operating expenses	254.4			172.3			177.6			186.8
	Operating income	58.5			103.2			111.1			141.7
	Interest expense, net	41.1			40.9			40.6			40.3
	Other expense (income)	0.5			0.6			—			(0.2		)
	Income before income taxes	16.9			61.7			70.5			101.6
	Income taxes	0.2			—			0.1			0.2
	Net income	16.7			61.7			70.4			101.4
	Net loss attributable to	(2.8		)	(0.6		)	(0.1		)	—
	noncontrolling interests
	Net income attributable to	$	19.5		$	62.3		$	70.5		$	101.4
	controlling interests
	Basic net income per unit:
	Common units	$	0.08		$	0.27		$	0.28		$	0.42
	Class B units	$	(0.02	)	$	(0.32	)	$	0.03		$	0.19
	Diluted net income per unit:
	Common units	$	0.08		$	0.21		$	0.28		$	0.42
	Class B units	$	—		$	—		$	0.03		$	0.19

Guarantee_of_Securities_of_Sub1

Guarantee of Securities of Subsidiaries (Tables)	12 Months Ended
	Dec. 31, 2014
Condensed Financial Information of Parent Company Only Disclosure [Abstract]
Condensed Consolidated Balance Sheet	Condensed Consolidating Balance Sheets as of December 31, 2014
	(Millions)
	Assets		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer
	Cash and cash equivalents		$	0.5		$	1.8		$	4.3		$	—			$	6.6
	Receivables		—			—			110.9			—				110.9
	Receivables - affiliate		—			—			9			(9.0		)		—
	Gas and liquids stored underground		—			—			4.1			—				4.1
	Prepayments		0.1			—			14.4			—				14.5
	Advances to affiliates		—			6.3			106.2			(112.5		)		—
	Other current assets		0.5			—			19.2			(6.2		)		13.5
	Total current assets		1.1			8.1			268.1			(127.7		)		149.6
	Investment in consolidated subsidiaries		1,970.60			6,744.10			—			(8,714.7		)		—
	Property, plant and equipment, gross		0.6			—			9,355.00			—				9,355.60
	Less–accumulated depreciation and		0.6			—			1,765.80			—				1,766.40
	amortization
	Property, plant and equipment, net		—			—			7,589.20			—				7,589.20
	Other noncurrent assets		—			3.4			465.2			(0.6		)		468
	Advances to affiliates – noncurrent		2,148.30			212			996.5			(3,356.8		)		—
	Total other assets		2,148.30			215.4			1,461.70			(3,357.4		)		468
	Total Assets		$	4,120.00		$	6,967.60		$	9,319.00		$	(12,199.8	)		$	8,206.80
	Liabilities and Equity		Parent			Subsidiary			Non-guarantor			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer			Subsidiaries
	Payables		$	0.2		$	0.1		$	61.8		$	—			$	62.1
	Payable to affiliates		1.5			—			9			(9.0		)		1.5
	Advances from affiliates		—			106.2			6.3			(112.5		)		—
	Other current liabilities		—			21.4			141.7			(6.5		)		156.6
	Total current liabilities		1.7			127.7			218.8			(128.0		)		220.2
	Total long-term debt and capital lease		—			1,724.50			1,965.20			—				3,689.70
	obligation
	Payable to affiliate - noncurrent		16			—			—			—				16
	Advances from affiliates - noncurrent		—			3,144.80			212			(3,356.8		)		—
	Other noncurrent liabilities		—			—			178.9			(0.3		)		178.6
	Total other liabilities and deferred		16			3,144.80			390.9			(3,357.1		)		194.6
	credits
	Total partners’ capital		4,102.30			1,970.60			6,744.10			(8,714.7		)		4,102.30
	Noncontrolling interest		—			—			—			—				—
	Total Equity		4,102.30			1,970.60			6,744.10			(8,714.7		)		4,102.30
	Total Liabilities and Equity		$	4,120.00		$	6,967.60		$	9,319.00		$	(12,199.8	)		$	8,206.80
	Condensed Consolidating Balance Sheets as of December 31, 2013
	(Millions)
	Assets		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer
	Cash and cash equivalents		$	0.2		$	9.2		$	19.1		$	—			$	28.5
	Receivables		—			—			119.2			—				119.2
	Receivables - affiliate		0.1			0.1			14.3			(13.4		)		1.1
	Gas and liquids stored underground		—			—			0.7			—				0.7
	Prepayments		0.3			—			12.6			—				12.9
	Advances to affiliates		—			—			194.4			(194.4		)		—
	Other current assets		—			—			23.8			(9.1		)		14.7
	Total current assets		0.6			9.3			384.1			(216.9		)		177.1
	Investment in consolidated subsidiaries		1,480.80			6,138.30			—			(7,619.1		)		—
	Property, plant and equipment, gross		0.6			—			8,722.70			—				8,723.30
	Less–accumulated depreciation		0.6			—			1,488.60			—				1,489.20
	and amortization
	Property, plant and equipment, net		—			—			7,234.10			—				7,234.10
	Other noncurrent assets		0.3			3.7			420.7			—				424.7
	Advances to affiliates – noncurrent		2,512.10			168.7			733.1			(3,413.9		)		—
	Investment in unconsolidated affiliates		—			—			78.6			—				78.6
	Total other assets		2,512.40			172.4			1,232.40			(3,413.9		)		503.3
	Total Assets		$	3,993.80		$	6,320.00		$	8,850.60		$	(11,249.9	)		$	7,914.50
	Liabilities and Equity		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
			Guarantor			Issuer
	Payables		$	0.2		$	—		$	70.6		$	—			$	70.8
Payable to affiliates		0.7			—			13.9			(13.4		)		1.2
Advances from affiliates		—			194.4			—			(194.4		)		—
Other current liabilities		—			19.7			153.3			(9.0		)		164
Total current liabilities		0.9			214.1			237.8			(216.8		)		236
Total long-term debt and capital lease		—			1,379.90			2,044.50			—				3,424.40
obligation
Payable to affiliate - noncurrent		16			—			—			—				16
Advances from affiliates - noncurrent		—			3,245.20			168.7			(3,413.9		)		—
Other noncurrent liabilities		—			—			174.8			(0.1		)		174.7
Total other liabilities and deferred		16			3,245.20			343.5			(3,414.0		)		190.7
credits
Total partners’ capital		3,976.90			1,480.80			6,138.30			(7,619.1		)		3,976.90
Noncontrolling interest		—			—			86.5			—				86.5
Total Equity		3,976.90			1,480.80			6,224.80			(7,619.1		)		4,063.40
Total Liabilities and Equity		$	3,993.80		$	6,320.00		$	8,850.60		$	(11,249.9	)		$	7,914.50
Condensed Consolidating Statements of Income	Condensed Consolidating Statements of Income for the Year Ended December 31, 2014
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Operating Revenues:
	Transportation	$	—		$	—		$	1,157.90		$	(92.8	)		$	1,065.10
	Parking and lending	—			—			23.3			—				23.3
	Storage	—			—			90.4			(0.9		)		89.5
	Other	—			—			55.9			—				55.9
	Total operating revenues	—			—			1,327.50			(93.7		)		1,233.80
	Operating Costs and Expenses:
	Fuel and transportation	—			—			214.4			(93.7		)		120.7
	Operation and maintenance	—			—			198.8			—				198.8
	Administrative and general	0.2			—			124.8			—				125
	Other operating costs and expenses	0.2			—			391			—				391.2
	Total operating costs and expenses	0.4			—			929			(93.7		)		835.7
	Operating (loss) income	(0.4		)	—			398.5			—				398.1
	Other Deductions (Income):
	Interest expense	—			76.5			89			—				165.5
	Interest (income) expense - affiliates, net	(30.0		)	41.2			(11.2		)	—				—
	Interest income	—			—			(0.6		)	—				(0.6		)
	Equity in earnings of subsidiaries	(204.0		)	(321.7		)	—			525.7				—
	Equity losses in unconsolidated	—			—			86.5			—				86.5
	affiliates
	Miscellaneous other income, net	—			—			(0.5		)	—				(0.5		)
	Total other (income) deductions	(234.0		)	(204.0		)	163.2			525.7				250.9
	Income (loss) before income taxes	233.6			204			235.3			(525.7		)		147.2
	Income taxes	—			—			0.4			—				0.4
	Net income (loss)	233.6			204			234.9			(525.7		)		146.8
	Net loss attributable to noncontrolling	—			—			(86.8		)	—				(86.8		)
	interests
	Net income (loss) attributable to controlling	$	233.6		$	204		$	321.7		$	(525.7	)		$	233.6
	interests
	Condensed Consolidating Statements of Income for the Year Ended December 31, 2013
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Operating Revenues:
	Transportation	$	—		$	—		$	1,116.40		$	(88.4	)		$	1,028.00
	Parking and lending	—			—			24			(0.1		)		23.9
	Storage	—			—			111			(0.1		)		110.9
	Other	—			—			42.8			—				42.8
	Total operating revenues	—			—			1,294.20			(88.6		)		1,205.60
	Operating Costs and Expenses:
	Fuel and transportation	—			—			182			(88.6		)		93.4
	Operation and maintenance	—			0.3			186.2			—				186.5
	Administrative and general	(0.1		)	0.8			116.7			—				117.4
	Other operating costs and expenses	0.3			0.1			393.4			—				393.8
	Total operating costs and expenses	0.2			1.2			878.3			(88.6		)		791.1
	Operating (loss) income	(0.2		)	(1.2		)	415.9			—				414.5
	Other Deductions (Income):
	Interest expense	—			72.7			90.7			—				163.4
	Interest (income) expense - affiliates, net	(33.6		)	41.3			(7.7		)	—				—
	Interest income	—			—			(0.5		)	—				(0.5		)
	Equity in earnings of subsidiaries	(220.3		)	(335.5		)	—			555.8				—
	Equity losses in unconsolidated affiliates	—			—			1.2			—				1.2
	Miscellaneous other income, net	—			—			(0.3		)	—				(0.3		)
	Total other (income) deductions	(253.9		)	(221.5		)	83.4			555.8				163.8
	Income (loss) before income taxes	253.7			220.3			332.5			(555.8		)		250.7
	Income taxes	—			—			0.5			—				0.5
	Net income (loss)	253.7			220.3			332			(555.8		)		250.2
	Net loss attributable to noncontrolling	—			—			(3.5		)	—				(3.5		)
	interests
	Net income (loss) attributable to controlling	$	253.7		$	220.3		$	335.5		$	(555.8	)		$	253.7
interests
Condensed Consolidating Statements of Income for the Year Ended December 31, 2012
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Operating Revenues:
Transportation	$	—		$	—		$	1,147.50		$	(89.2	)		$	1,058.30
Parking and lending	—			—			28.7			(0.7		)		28
Storage	—			—			85.4			(0.7		)		84.7
Other	—			—			14			—				14
Total operating revenues	—			—			1,275.60			(90.6		)		1,185.00
Operating Costs and Expenses:
Fuel and transportation	—			—			170			(90.6		)		79.4
Operation and maintenance	—			—			167.2			—				167.2
Administrative and general	0.5			—			114.8			—				115.3
Other operating costs and expenses	0.3			—			349			—				349.3
Total operating costs and expenses	0.8			—			801			(90.6		)		711.2
Operating (loss) income	(0.8		)	—			474.6			—				473.8
Other Deductions (Income):
Interest expense	—			63.1			98.4			—				161.5
Interest (income) expense - affiliates, net	(35.6		)	52.9			(10.4		)	—				6.9
Interest income	—			—			(0.7		)	—				(0.7		)
Equity in earnings of subsidiaries	(271.2		)	(387.2		)	—			658.4				—
Miscellaneous other income, net	—			—			(0.4		)	—				(0.4		)
Total other (income) deductions	(306.8		)	(271.2		)	86.9			658.4				167.3
Income (loss) before income taxes	306			271.2			387.7			(658.4		)		306.5
Income taxes	—			—			0.5			—				0.5
Net income (loss)	306			271.2			387.2			(658.4		)		306
Net loss attributable to noncontrolling	—			—			—			—				—
interests
Net income (loss) attributable to controlling	$	306		$	271.2		$	387.2		$	(658.4	)		$	306
interests
Condensed Consolidating Statements of Comprehensive Income	Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2014
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Net income (loss)	$	233.6		$	204		$	234.9		$	(525.7	)		$	146.8
	Other comprehensive income (loss):
	(Loss) gain on cash flow hedges	(0.7		)	(0.7		)	(0.7		)	1.4				(0.7		)
	Reclassification adjustment transferred to	2.6			2.6			0.9			(3.5		)		2.6
	Net income from cash flow hedges
	Pension and other postretirement	(10.9		)	(10.9		)	(10.9		)	21.8				(10.9		)
	benefit costs
	Total Comprehensive Income (Loss)	224.6			195			224.2			(506.0		)		137.8
	Comprehensive loss attributable to	—			—			(86.8		)	—				(86.8		)
	noncontrolling interests
	Comprehensive income (loss)	$	224.6		$	195		$	311		$	(506.0	)		$	224.6
	attributable to controlling interests
	Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2013
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Net income (loss)	$	253.7		$	220.3		$	332		$	(555.8	)		$	250.2
	Other comprehensive income (loss):
	Gain (loss) on cash flow hedges	1.6			1.6			1.6			(3.2		)		1.6
	Reclassification adjustment transferred to	1.2			1.2			(0.5		)	(0.7		)		1.2
	Net income from cash flow hedges
	Pension and other postretirement	0.7			0.7			0.7			(1.4		)		0.7
	benefit costs
	Total Comprehensive Income (Loss)	257.2			223.8			333.8			(561.1		)		253.7
	Comprehensive loss attributable to	—			—			(3.5		)	—				(3.5		)
	noncontrolling interests
	Comprehensive income (loss)	$	257.2		$	223.8		$	337.3		$	(561.1	)		$	257.2
	attributable to controlling interests
	Condensed Consolidating Statements of Comprehensive Income for the Year Ended December 31, 2012
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Net income (loss)	$	306		$	271.2		$	387.2		$	(658.4	)		$	306
	Other comprehensive income (loss):
	(Loss) gain on cash flow hedges	(7.1		)	(7.1		)	(6.7		)	13.8				(7.1		)
	Reclassification adjustment transferred to	2			2			0.3			(2.3		)		2
	Net Income from cash flow hedges
	Pension and other postretirement	(12.8		)	(12.8		)	(12.8		)	25.6				(12.8		)
	benefit costs
	Total Comprehensive Income (Loss)	288.1			253.3			368			(621.3		)		288.1
	Comprehensive loss attributable to	—			—			—			—				—
	noncontrolling interests
	Comprehensive income (loss) attributable to	$	288.1		$	253.3		$	368		$	(621.3	)		$	288.1
	controlling interests
Condensed Consolidating Statements of Cash Flows	Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2014
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Net cash provided by (used in)	$	30.2		$	(112.1	)	$	595.5		$	—			$	513.6
	operating activities
	INVESTING ACTIVITIES:
	Capital expenditures	—			—			(404.4		)	—				(404.4		)
	Proceeds from sale of operating assets	—			—			2.9			—				2.9
	Proceeds from insurance and other	—			—			6.3			—				6.3
	recoveries
	Advances to affiliates, net	363.9			(49.6		)	(175.2		)	(139.0		)		0.1
	Investment in unconsolidated affiliates	—			—			(20.5		)	—				(20.5		)
	Distribution from unconsolidated	—			—			11.1			—				11.1
	affiliates
	Acquisition of businesses, net of cash	(294.7		)	—			—			—				(294.7		)
	acquired
	Net cash provided by (used in)	69.2			(49.6		)	(579.8		)	(139.0		)		(699.2		)
	investing activities
	FINANCING ACTIVITIES:
	Proceeds from long-term debt, net of issuance cost	—			342.9			—			—				342.9
	Proceeds from borrowings on revolving	—			—			665			—				665
	credit agreement
	Repayment of borrowings on revolving	—			—			(720.0		)	—				(720.0		)
	credit agreement
	Repayment of borrowings from term	—			—			(25.0		)	—				(25.0		)
	loan
	Principal payment of capital lease	—			—			(0.4		)	—				(0.4		)
	obligation
	Advances from affiliates, net	0.1			(188.6		)	49.6			139				0.1
	Distributions paid	(99.2		)	—			—			—				(99.2		)
	Capital contribution from noncontrolling	—			—			8.2			—				8.2
	interests
	Distributions paid to noncontrolling	—			—			(7.9		)	—				(7.9		)
	interests
	Net cash (used in) provided by	(99.1		)	154.3			(30.5		)	139				163.7
	financing activities
	Increase (decrease) in cash and cash equivalents	0.3			(7.4		)	(14.8		)	—				(21.9		)
	Cash and cash equivalents at	0.2			9.2			19.1			—				28.5
	beginning of period
	Cash and cash equivalents at	$	0.5		$	1.8		$	4.3		$	—			$	6.6
	end of period
	Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2013
	(Millions)
		Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
		Guarantor			Issuer
	Net cash provided by (used in)	$	33.9		$	(108.8	)	$	609.2		$	—			$	534.3
	operating activities
	INVESTING ACTIVITIES:
	Capital expenditures	—			—			(294.8		)	—				(294.8		)
	Proceeds from sale of operating assets	—			—			60.7			—				60.7
	Proceeds from insurance and other	—			—			1.4			—				1.4
	recoveries
	Advances to affiliates, net	126.4			(84.3		)	(342.8		)	300.7				—
	Investment in consolidated affiliates	—			(15.1		)	—			15.1				—
	Investment in unconsolidated affiliates	—			—			(76.7		)	—				(76.7		)
	Net cash provided by (used in)	126.4			(99.4		)	(652.2		)	315.8				(309.4		)
	investing activities
	FINANCING ACTIVITIES:
	Proceeds from borrowings on revolving	—			—			1,128.00			—				1,128.00
	credit agreement
	Repayment of borrowings on revolving	—			—			(1,255.0		)	—				(1,255.0		)
	credit agreement
	Contribution from parent	—			—			15.1			(15.1		)		—
Principal payment of capital lease	—			—			(0.2		)	—				(0.2		)
obligation
Advances from affiliates, net	(2.8		)	216.4			84.3			(300.7		)		(2.8		)
Distributions paid	(533.9		)	—			—			—				(533.9		)
Capital contribution from noncontrolling	—			—			87.1			—				87.1
interests
Proceeds from sale of common units	368.7			—			—			—				368.7
Capital contribution from general partner	7.8			—			—			—				7.8
Net cash (used in) provided by	(160.2		)	216.4			59.3			(315.8		)		(200.3		)
financing activities
Increase in cash and cash equivalents	0.1			8.2			16.3			—				24.6
Cash and cash equivalents at	0.1			1			2.8			—				3.9
beginning of period
Cash and cash equivalents at	$	0.2		$	9.2		$	19.1		$	—			$	28.5
end of period
Condensed Consolidating Statements of Cash Flow for the Year Ended December 31, 2012
(Millions)
	Parent			Subsidiary			Non-guarantor Subsidiaries			Eliminations				Consolidated Boardwalk Pipeline Partners, LP
	Guarantor			Issuer
Net cash provided by (used in)	$	31.4		$	577.9		$	655.7		$	(689.5	)		$	575.5
operating activities
INVESTING ACTIVITIES:
Capital expenditures	—			—			(226.9		)	—				(226.9		)
Proceeds from sale of operating assets	—			—			5.9			—				5.9
Proceeds from insurance and other	—			—			10.4			—				10.4
recoveries
Advances to affiliates, net	(404.2		)	(84.4		)	66.2			422.4				—
Investment in consolidated affiliates	(17.0		)	(398.0		)	—			415				—
Acquisition of businesses, net of cash	—			—			(620.2		)	—				(620.2		)
acquired
Net cash (used in) provided by	(421.2		)	(482.4		)	(764.6		)	837.4				(830.8		)
investing activities
FINANCING ACTIVITIES:
Proceeds from long-term debt and term	—			297.6			520.4			—				818
loans
Repayment of borrowings from	—			(100.0		)	(425.0		)	—				(525.0		)
long-term debt, term loans and
subordinated debt
Proceeds from borrowings on revolving	—			300			1,835.00			—				2,135.00
credit agreement
Repayment of borrowings on revolving	—			(403.8		)	(1,891.5		)	—				(2,295.3		)
credit agreement including financing
costs
Contribution from parent	—			17			398			(415.0		)		—
Contribution received related to	—			—			269.2			—				269.2
predecessor equity
Repayment of contribution received	—			(554.0		)	—			—				(554.0		)
related to predecessor equity
Advances from affiliate	2.6			338			84.4			(422.4		)		2.6
Distributions paid	(478.9		)	—			(689.5		)	689.5				(478.9		)
Proceeds from sale of common units	847.7			—			—			—				847.7
Capital contribution from general	18			—			—			—				18
partner
Net cash provided by (used in)	389.4			(105.2		)	101			(147.9		)		237.3
financing activities
Decrease in cash and cash equivalents	(0.4		)	(9.7		)	(7.9		)	—				(18.0		)
Cash and cash equivalents at	0.5			10.7			10.7			—				21.9
beginning of period
Cash and cash equivalents at	$	0.1		$	1		$	2.8		$	—			$	3.9
end of period

Corporate_Structure_Details

Corporate Structure (Details)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 20, 2015
In Millions, unless otherwise specified
Corporate Structure [Line Items]
Percent of General Partner Interest Owned by Holding Company	2.00%	2.00%	2.00%
Subsequent Event | Boardwalk Pipelines Holding Company
Corporate Structure [Line Items]
Number of the Partnership's common units owned by holding company (in units)				125.6
Percentage of Partnership's equity interests owned by holding company (in hundredths)				53.00%
Subsequent Event | Boardwalk GP, LP
Corporate Structure [Line Items]
Percent of General Partner Interest Owned by Holding Company				2.00%

Accounting_Policies_Details

Accounting Policies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
	segments
Accounting Policies [Line Items]
Restricted Cash and Cash Equivalents	$0	$0
Materials And Supplies Held In Other Assets	15.3	12.8
Number of Reportable Segments (in ones)	1
Capitalized interest and allowance for borrowed funds used during construction	6.8	6.4	4.7
Allowance for equity funds used during construction	0.5	0.2	0.4
Deferred revenues related to PAL and interruptible storage services	1	7.9
Deferred revenues related to a firm transportation agreement	6.2	4.6
Deferred revenues related to a brine supply contract	2.5
Retained fuel included in Transportation	90.3	76.9	71.8
Contractual Retainage Provision (Percentage)	0.50%
Customer Refund Liability, Current	0	0
Unrealized Gain (Loss) on Cash Flow Hedging Instruments	$0	$0	$0
Minimum [Member]
Accounting Policies [Line Items]
Equity Method Investment, Ownership Percentage	20.00%
Maximum [Member]
Accounting Policies [Line Items]
Equity Method Investment, Ownership Percentage	50.00%

Accounting_Policies_Schedule_o

Accounting Policies Schedule of Property, Plant and Equipment (Details)	12 Months Ended
	Dec. 31, 2014
Minimum [Member]
Property, Plant and Equipment [Line Items]
Depreciation range for PPE related to operations for which regulatory accounting does not apply (in years)	3 years
Depreciation range for PPE related to operations for which regulatory accounting is applicable (in years)	5 years
Maximum [Member]
Property, Plant and Equipment [Line Items]
Depreciation range for PPE related to operations for which regulatory accounting does not apply (in years)	35 years
Depreciation range for PPE related to operations for which regulatory accounting is applicable (in years)	62 years

Investments_Details

Investments (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Variable Interest Entity [Line Items]
Income (Loss) from Equity Method Investments	$0	$0	$0	$0	$0	$0	$0	$0	($86.50)	($1.20)	$0
Cash and Cash Equivalents, at Carrying Value	6.6				28.5				6.6	28.5	3.9	21.9
Investment in unconsolidated affiliates	0				78.6				0	78.6
Construction work in progress	105.5				174.5				105.5	174.5
Payables	62.1				70.8				62.1	70.8
Boardwalk Bluegrass and Boardwalk Moss Lake, Bluegrass Pipeline, Moss Lake Fractionation and Moss Lake LPG [Member] | Boardwalk Pipeline Partners, LP
Variable Interest Entity [Line Items]
Total Project Related Impairment				92.9
Income (Loss) from Impairment Attributable to Noncontrolling Interest				-82.9
Income (Loss) from Equity Method Investments				-10
Bluegrass Pipeline, Moss Lake Fractionation and Moss Lake LPG [Member] | Boardwalk Bluegrass and Boardwalk Moss Lake
Variable Interest Entity [Line Items]
Cash and Cash Equivalents, at Carrying Value					15					15
Investment in unconsolidated affiliates	0				78.6				0	78.6
Construction work in progress					6.8					6.8
Payables					$4.90					$4.90

Acquisition_of_Boardwalk_Petro2

Acquisition of Boardwalk Petrochemical (Details) (USD $)	3 Months Ended								12 Months Ended			0 Months Ended		3 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Oct. 08, 2014		Dec. 31, 2014
Business Acquisition [Line Items]
Goodwill	$237.40				$215.50				$237.40	$215.50	$267			$237.40
Revenues	304.6	278.9	293.4	356.9	312.9	275.5	288.7	328.5	1,233.80	1,205.60	1,185
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest	-36.9	-28.4	-55.9	-25.6	-16.7	-61.7	-70.4	-101.4	-146.8	-250.2	-306
Boardwalk Petrochemical/Evangeline [Member]
Business Acquisition [Line Items]
Business Acquisition, Date of Acquisition Agreement												8-Oct-14
Business Acquisition, Cost of Acquired Entity, Cash Paid												294.7
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Property, Plant, and Equipment												253.3	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill												20	[1],[2]
Goodwill												21.9	[1],[3]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Assets												295.2	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities												-0.3	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Noncurrent Liabilities												-0.2	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Liabilities												-0.5	[1]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net												294.7	[1]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life												30 years
Revenues														0.7
Net Income (Loss), Including Portion Attributable to Noncontrolling Interest														1.8
Business Combination, Acquisition Related Costs														$2.60
[1]	The purchase price allocation is preliminary and is subject to change based on the final working capital adjustments which are expected to be settled in the first quarter 2015. For the period from October 8, 2014 to December 31, 2014, Evangeline contributed $0.7 million to the Partnership’s revenues and decreased the Partnership's net income by $1.8 million, excluding acquisition costs. The Partnership incurred $2.6 million of costs related to the acquisition of Boardwalk Petrochemical, which were expensed as incurred and were recorded in Administrative and general expenses. Pro forma data is not provided because the impact of the acquisition on the Partnership’s revenues and net income was not material.
[2]	Customer-based intangibles are estimated to have a weighted-average useful life of 30 years.
[3]	Goodwill represents the excess of the purchase price over the estimated fair value of the assets acquired, net of the fair value of the liabilities assumed in the acquisition.

Commitments_and_Contingencies_1

Commitments and Contingencies Legal Proceedings and Settlements (Details)	12 Months Ended
	Dec. 31, 2014
	class_action_suit
	lawsuits
Whistler Junction Matter
Loss Contingencies [Line Items]
Number of Lawsuits Filed (in ones)	10
Number of Class Action Lawsuits Filed (in ones)	1
Southeast Louisiana Flood Protection Litigation
Loss Contingencies [Line Items]
Loss Contingency, Number of Defendants (in ones)	100

Commitments_and_Contingencies_2

Commitments and Contingencies (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
	t
	facilities
Environmental and Safety Matters [Line Items]
Accrual for Environmental Loss Contingencies	$6.10	$6.50
Number of years the related expenditures are expected to cover assessment and remediation costs (in years)	7
Accrued Environmental Loss Contingencies, Current	1.5	1.5
Accrued Environmental Loss Contingencies, Noncurrent	4.6	5
Number of facilities operated affected by non-attainment requirements	2
Minimum volume of annual greenhouse gas emissions to be reported (in tons)	25,000
Target Methane Reductions	45.00%
Commitments for Construction [Abstract]
Purchase Commitment, Remaining Minimum Amount Committed	$61.90

Commitments_and_Contingencies_3

Commitments and Contingencies Schedule of Operating Leased Assets (Details) (Office Space and Equipment Rentals [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Office Space and Equipment Rentals [Member]
Operating Leased Assets [Line Items]
Operating Leases, Rent Expense	$10.70	$8.60	$6.40
2015	4.7
2016	4.4
2017	3.9
2018	3.3
2019	2.9
Thereafter	13.6
Total	$32.80

Commitments_and_Contingencies_4

Commitments and Contingencies Schedule of Pipeline Capacity Agreements (Details) (Pipeline Capacity Agreements [Member], USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pipeline Capacity Agreements [Member]
Recorded Unconditional Purchase Obligation [Line Items]
Expenses related to pipeline capacity agreements	$10.10	$9.80	$9.10
2015	6.9
2016	6.3
2017	6.2
2018	2
2019	0
Thereafter	0
Total	$21.40

Commitments_and_Contingencies_5

Commitments and Contingencies Schedule of Capital Leased Assets (Details) (USD $)	12 Months Ended			3 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Sep. 30, 2013
Capital Leased Assets [Line Items]
Capital Lease Obligations Incurred	$0	$10.50	$0
Long-term obligations under capital lease	9.6	10
Office Building [Member]
Capital Leased Assets [Line Items]
Description of Lessee Leasing Arrangements, Capital Leases	The office building lease has a term of fifteen years with two twenty year renewal options.
Capital Lease Obligations Incurred				10.5
2015	1
2016	1
2017	1
2018	1
2019	1.1
Thereafter	9.5
Total minimum lease payments	14.6
Less amounts representing interest	-4.6
Present value of obligation under capital lease	10
Less: current portion of obligations under capital lease (recorded in Other current liabilities)	-0.4
Long-term obligations under capital lease	9.6
Capital Leases, Income Statement, Amortization Expense	0.7	0.3
Capital Leased Assets, Gross	10.5	10.5
Capital Leases, Lessee Balance Sheet, Assets by Major Class, Accumulated Depreciation	$1	$0.30

Fair_Value_Measurements_Deriva3

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI) Fair Value Measurements Assets and Liabilities Measured on Recurring and Nonrecurring (Details) (USD $)	3 Months Ended
In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in unconsolidated affiliates		$0	$78.60
Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Impairment of Long-Lived Assets Held-for-use	7.1
Equity Method Investment, Other than Temporary Impairment	85.8
Income (Loss) from Impairment Attributable to Noncontrolling Interest	-82.9
Income (Loss) from Impairments Attributable to Parent	-10
Fair Value, Inputs, Level 2 | Commodity Contract
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Recurring		0	0.5
Liabilities, Fair Value Disclosure, Recurring		0	0
Bluegrass Pipeline, Moss Lake Fractionation and Moss Lake LPG [Member] | Boardwalk Bluegrass and Boardwalk Moss Lake
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Investment in unconsolidated affiliates		$0	$78.60

Fair_Value_Measurements_Deriva4

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI) Other Comprehensive Income (OCI) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	$3.50
Accumulated other comprehensive income (loss) (beginning)	-63.8		-67.3		-49.4
Gain (loss) recorded in accumulated other comprehensive income	-0.7		1.6		-7.1
Transportation operating revenues	-1,065.10		-1,028		-1,058.30
Interest Expense	165.5		163.4		161.5
Pension and other postretirement benefit costs	-10.9		0.7		-12.8
Accumulated other comprehensive income (loss) (ending)	-72.8		-63.8		-67.3
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transportation operating revenues			0.1
Other operating revenues	0.2		-0.1		-0.1
Disposal of assets			-1.2
Interest Expense	2.4	[1]	2.4	[1]	2.1	[1]
Net gain on disposal of operating assets
Accumulated Other Comprehensive Income (Loss) [Line Items]
Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months	-2.4
Accumulated other comprehensive income (loss) (beginning)	-12.7		-15.5		-10.4
Gain (loss) recorded in accumulated other comprehensive income	-0.7		1.6		-7.1
Pension and other postretirement benefit costs	0		0		0
Accumulated other comprehensive income (loss) (ending)	-10.8		-12.7		-15.5
Net gain on disposal of operating assets | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transportation operating revenues			0.1
Other operating revenues	0.2		-0.1		-0.1
Disposal of assets			-1.2
Interest Expense	2.4	[1]	2.4	[1]	2.1	[1]
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Defined Benefit Plan, Amortization of Prior Service Cost (Credit)	5.9
Accumulated other comprehensive income (loss) (beginning)	-51.1		-51.8		-39
Gain (loss) recorded in accumulated other comprehensive income	0		0		0
Pension and other postretirement benefit costs	-10.9		0.7		-12.8
Accumulated other comprehensive income (loss) (ending)	-62		-51.1		-51.8
Accumulated Defined Benefit Plans Adjustment [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Transportation operating revenues			0
Other operating revenues	0		0		0
Disposal of assets			0
Interest Expense	$0	[1]	$0	[1]	$0	[1]
[1]	Related to amounts deferred in AOCI from Treasury rate locks described above.

Fair_Value_Measurements_Deriva5

Fair Value Measurements, Derivatives and Other Comprehensive Income (OCI) Financial Assets and Liabilities (Details) (USD $)	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	$6.60		$28.50		$3.90	$21.90
Capital Lease Obligations, Noncurrent	9.6		10
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value	6.6		28.5
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Fair Value	3,787.40		3,573.80
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and Cash Equivalents, at Carrying Value	6.6		28.5
Long-term Debt	3,680.10	[1]	3,414.40	[2]
Fair Value | Fair Value, Inputs, Level 1
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value	6.6		28.5
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Fair Value	0		0
Fair Value | Fair Value, Inputs, Level 2
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value	0		0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Fair Value	3,787.40		3,573.80
Fair Value | Fair Value, Inputs, Level 3
Financial Instruments, Financial Assets, Balance Sheet Groupings [Abstract]
Cash and Cash Equivalents, Fair Value	0		0
Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Fair Value	$0		$0
[1]	The carrying amount of long-term debt excludes a $9.6 million long-term capital lease obligation.
[2]	The carrying amount of long-term debt excludes a $10.0 million long-term capital lease obligation.

Property_Plant_and_Equipment_P2

Property, Plant and Equipment (PPE) Property, Plant and Equipment Class and Useful Life (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Property, Plant and Equipment [Line Items]
Total PPE	$9,355.60	$8,723.30
Less: accumulated depreciation	1,766.40	1,489.20
Total PPE, net	7,589.20	7,234.10
Depreciable plant:
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	37 years	36 years
Total PPE	9,099.90	8,414.80
Depreciable plant: | Transmission
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	37 years	37 years
Total PPE	7,719.80	7,067.70
Depreciable plant: | Storage
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	38 years	38 years
Total PPE	758.5	749.7
Depreciable plant: | Gathering
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	27 years	27 years
Total PPE	336.7	326
Depreciable plant: | General
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	14 years	13 years
Total PPE	170	160.3
Depreciable plant: | Rights of way and other
Property, Plant and Equipment [Line Items]
Property, Plant and Equipment, Weighted-Average Useful Life	36 years	35 years
Total PPE	114.9	111.1
Non-depreciable:
Property, Plant and Equipment [Line Items]
Total PPE	255.7	308.5
Non-depreciable: | Storage
Property, Plant and Equipment [Line Items]
Total PPE	105.5	90.8
Non-depreciable: | Construction work in progress
Property, Plant and Equipment [Line Items]
Total PPE	105.5	174.5
Non-depreciable: | Land
Property, Plant and Equipment [Line Items]
Total PPE	28.4	26.9
Non-depreciable: | Other
Property, Plant and Equipment [Line Items]
Total PPE	$16.30	$16.30

Property_Plant_and_Equipment_P3

Property, Plant and Equipment (PPE) Undivided Interests (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Undivided Interest Property [Line Items]
Gross PPE Investment	$130.90	$120.70
Accumulated Depreciation	37	32.9
Bistineau Storage
Undivided Interest Property [Line Items]
Undivided interests in storage facility	92.00%
Gross PPE Investment	64.3	55.8
Accumulated Depreciation	17.5	15.1
Mobile Bay Pipeline
Undivided Interest Property [Line Items]
Undivided interest in pipeline	64.00%
Gross PPE Investment	13	11.1
Accumulated Depreciation	3.6	3.1
NGL pipelines and facilities
Undivided Interest Property [Line Items]
Undivided interest in Ethylene Wells	83.00%
Gross PPE Investment	34.8	34.8
Accumulated Depreciation	2.2	1.3
Offshore and Other Assets
Undivided Interest Property [Line Items]
Gross PPE Investment	18.8	19
Accumulated Depreciation	$13.70	$13.40

Property_Plant_and_Equipment_D

Property, Plant and Equipment (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Asset Dispositions and Impairments [Abstract]
Asset impairment	$10.10	$4.10	$9.10
Gas Storage Sale
Gas Sales [Abstract]
Gain (Loss) on Disposition of Other Assets		29.9
Volume Of Gas Sold (in MMcf)		14,900
Carrying Value Before Sale or Impairment		26
Carthage Compressor Station Incident
Compressor Station Fire [Abstract]
Recovery of Direct Costs	12.3
Insured Event, Gain (Loss)	$0.60	$1.70	$1.20

Goodwill_and_Intangible_Assets2

Goodwill and Intangible Assets Goodwill (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Goodwill [Roll Forward]
Goodwill Period Start	$215.50		$267
Goodwill, Impairment Loss	0		-51.5	0
Goodwill, Acquired During Period	21.9	[1]
Goodwill Period End	$237.40		$215.50	$267
[1]	Refer to Note 4 for further information on the acquisition of Boardwalk Petrochemical.

Goodwill_and_Intangible_Assets3

Goodwill and Intangible Assets Intangible Assets (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$59.40	$39.40
Accumulated amortization	-3.5	-2.1
Net carrying amount	55.9	37.3
Amortization of Intangible Assets	1.4	1.3	0.8
2015	2
2016	2
2017	2
2018	2
2019	2
Thereafter	$45.90
Finite-Lived Intangible Asset, Useful Life	29 years

Asset_Retirement_Obligations_A2

Asset Retirement Obligations (ARO) (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Asset Retirement Obligation, Roll Forward Analysis [Roll Forward]
Balance at beginning of year	$47.10	$39
Liabilities recorded	4.3	8
Liabilities settled	-6.9	-1.7
Accretion expense	1.8	1.8
Balance at end of year	46.3	47.1
Less: Current portion of asset retirement obligations	-6.4	-7.8
Long-term asset retirement obligations	39.9	39.3
Provision for other asset retirement	$60.50	$57.60

Regulatory_Assets_and_Liabilit2

Regulatory Assets and Liabilities (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Regulatory Assets and Liabilities Disclosure [Abstract]
Period of recovery-minimum (in years)	1 year
Period of recovery-maximum (in years)	18 years
Regulatory Assets [Line Items]
Regulatory Assets	$23.90	$26.80
Pension
Regulatory Assets [Line Items]
Regulatory Assets	10.6	10.6
Tax effect of AFUDC equity
Regulatory Assets [Line Items]
Regulatory Assets	3.5	3.9
Unamortized debt expense and premium on reacquired debt
Regulatory Assets [Line Items]
Regulatory Assets	9.6	11.5
Fuel tracker
Regulatory Assets [Line Items]
Regulatory Assets	$0.20	$0.80

Regulatory_Assets_and_Liabilit3

Regulatory Assets and Liabilities Regulatory Liabilities (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$94.10	$89.60
Cashout and fuel tracker
Regulatory Liabilities [Line Items]
Regulatory Liabilities	0.9	1.1
Provision for other asset retirement
Regulatory Liabilities [Line Items]
Regulatory Liabilities	60.5	57.6
Unamortized discount on long-term debt
Regulatory Liabilities [Line Items]
Regulatory Liabilities	-1.5	-1.8
Postretirement benefits other than pension
Regulatory Liabilities [Line Items]
Regulatory Liabilities	$34.20	$32.70

Financing_Details

Financing (Details) (USD $)	12 Months Ended			3 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2012		Dec. 31, 2014		Jun. 30, 2012		Sep. 30, 2012
Debt Instruments [Abstract]
Capital Lease Obligations, Noncurrent	$9.60	$10				$9.60
Debt and Capital Lease Obligations	3,704.60	3,435				3,704.60
Less: unamortized debt discount	-14.9	-10.6				-14.9
Total long-term debt and capital lease obligation	3,689.70	3,424.40				3,689.70
Repayments of Unsecured Debt	0	0	525
Debt Instrument, Redemption Price, Percentage	100.00%
Amended Credit Agreement 2012 | Federal Funds Effective Swap Rate
Line of Credit Facility [Abstract]
Debt Instrument, Description of Variable Rate Basis	federal funds
Amended Credit Agreement 2012 | Eurodollar
Line of Credit Facility [Abstract]
Debt Instrument, Description of Variable Rate Basis	one month Eurodollar Rate
Amended Credit Agreement 2012 | Base Rate
Line of Credit Facility [Abstract]
Debt Instrument, Description of Variable Rate Basis	base rate
Amended Credit Agreement 2012 | Prime Rate
Line of Credit Facility [Abstract]
Debt Instrument, Description of Variable Rate Basis	prime rate
Amended Credit Agreement 2012 | London Interbank Offered Rate (LIBOR)
Line of Credit Facility [Abstract]
Debt Instrument, Description of Variable Rate Basis	LIBOR
Unsecured Debt
Long-term Debt, Fiscal Year Maturity [Abstract]
2015	525					525
2016	250					250
2017	895					895
2018	185					185
2019	350					350
Thereafter	1,490					1,490
Total long-term debt	3,695					3,695
Debt Instruments [Abstract]
Debt, Weighted Average Interest Rate	5.31%	5.32%				5.31%
Debt Instrument, Redemption, Description	The Partnerships notes and debentures are redeemable, in whole or in part, at the Partnerships option at any time, at a redemption price equal to the greater of 100% of the principal amount of the notes to be redeemed or a make whole redemption price based on the remaining scheduled payments of principal and interest discounted to the date of redemption at a rate equal to the Treasury rate plus 20 to 50 basis points depending upon the particular issue of notes, plus accrued and unpaid interest, if any. Other customary covenants apply, including those concerning events of default.
Debt Instrument, Covenant Description	The indentures governing the notes and debentures have restrictive covenants which provide that, with certain exceptions, neither the Partnership nor any of its subsidiaries may create, assume or suffer to exist any lien upon any property to secure any indebtedness unless the debentures and notes shall be equally and ratably secured. All of the Partnership's debt obligations are unsecured.
Debt Instrument, Covenant Compliance	At December 31, 2014, Boardwalk Pipelines and its operating subsidiaries were in compliance with their debt covenants.
Unsecured Debt | Boardwalk Pipelines 5.88% Notes Due 2016
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	250	250				250
Debt Instruments [Abstract]
Interest Rate (in hundredths)	5.88%					5.88%
Unsecured Debt | Boardwalk Pipelines 5.50% Notes Due 2017
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	300	300				300
Debt Instruments [Abstract]
Interest Rate (in hundredths)	5.50%					5.50%
Unsecured Debt | Boardwalk Pipelines 5.20% Notes Due 2018
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	185	185				185
Debt Instruments [Abstract]
Interest Rate (in hundredths)	5.20%					5.20%
Unsecured Debt | Boardwalk Pipelines 5.75% Notes Due 2019
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	350	350				350
Debt Instruments [Abstract]
Interest Rate (in hundredths)	5.75%					5.75%
Unsecured Debt | Boardwalk Pipelines 3.375% Notes Due 2023
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	300	300				300
Debt Instruments [Abstract]
Debt Instrument, Date of Issuance				5-Nov-12
Debt Instrument, Amount of Issuance			300	300
Purchaser Discounts and Expenses				2.4
Net Proceeds				297.6	[1]
Interest Rate (in hundredths)	3.38%		3.38%	3.38%		3.38%
Maturity Date				1-Feb-23
Unsecured Debt | Boardwalk Pipelines 4.95% Notes Due 2024
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	350	0				350
Debt Instruments [Abstract]
Debt Instrument, Date of Issuance						19-Nov-14
Debt Instrument, Amount of Issuance	350					350
Purchaser Discounts and Expenses						7.1
Net Proceeds						342.9	[2]
Interest Rate (in hundredths)	4.95%					4.95%
Maturity Date						15-Dec-24
Unsecured Debt | Gulf South 5.05% Notes Due 2015
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	275	275				275
Debt Instruments [Abstract]
Interest Rate (in hundredths)	5.05%					5.05%
Unsecured Debt | Gulf South 6.30% Notes Due 2017
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	275	275				275
Debt Instruments [Abstract]
Interest Rate (in hundredths)	6.30%					6.30%
Unsecured Debt | Gulf South 4.00% Notes Due 2022
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	300	300				300
Debt Instruments [Abstract]
Debt Instrument, Date of Issuance								15-Jun-12
Debt Instrument, Amount of Issuance								300
Purchaser Discounts and Expenses								3.5
Net Proceeds								296.5	[3]
Interest Rate (in hundredths)	4.00%					4.00%		4.00%
Maturity Date								15-Jun-22
Unsecured Debt | Texas Gas 4.60% Notes Due 2015
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	250	250				250
Debt Instruments [Abstract]
Interest Rate (in hundredths)	4.60%					4.60%
Unsecured Debt | Texas Gas 4.50% Notes Due 2021
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	440	440				440
Debt Instruments [Abstract]
Interest Rate (in hundredths)	4.50%					4.50%
Unsecured Debt | Texas Gas 7.25% Debentures Due 2027
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	100	100				100
Debt Instruments [Abstract]
Interest Rate (in hundredths)	7.25%					7.25%
Unsecured Debt | Total Notes and Debentures
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	3,375	3,025				3,375
Unsecured Debt | Term Loan
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	200	225				200
Debt Instruments [Abstract]
Debt, Weighted Average Interest Rate	1.91%	1.92%				1.91%
Debt Instrument, Unused Borrowing Capacity, Amount	0					0
Debt Instrument, Amount of Issuance	225					225
Maturity Date	1-Oct-17
Unsecured Debt | Gulf South Notes Due 2012
Debt Instruments [Abstract]
Repayments of Unsecured Debt										225
Interest Rate (in hundredths)										5.75%
Maturity Date										15-Aug-12
Line of Credit
Debt Instruments [Abstract]
Debt, Weighted Average Interest Rate	1.54%	1.29%				1.54%
Line of Credit Facility [Abstract]
Long-term Line of Credit	120	175				120
Line of Credit Facility, Covenant Terms	The credit facility contains various restrictive covenants and other usual and customary terms and conditions, including restrictions regarding the incurrence of additional debt, the sale of assets and sale-leaseback transactions. The financial covenants under the credit facility require the Partnership and its subsidiaries to maintain, among other things, a ratio of total consolidated debt to consolidated EBITDA (as defined in the credit agreement) measured for the previous twelve months of not more than 5.0 to 1.0, or up to 5.5 to 1.0 for the three quarters following an acquisition.
Line of Credit Facility, Covenant Compliance	The Partnership and its subsidiaries were in compliance with all covenant requirements under the credit facility as of December 31, 2014.
Maximum Ratio of Debt to EBITDA	5.0 to 1.0
Maximum Ratio of Debt to EBITDA after Acquisition	5.5 to 1.0
Line of Credit | Gulf Crossing Revolving Credit Facility
Long-term Debt, Fiscal Year Maturity [Abstract]
Total long-term debt	120	175				120
Line of Credit | Amended Credit Agreement 2012
Line of Credit Facility [Abstract]
Line of Credit Facility, Maximum Borrowing Capacity	1,000					1,000
Line of Credit Facility, Expiration Date	27-Apr-17
Line of Credit | Amended Credit Agreement 2012 | Minimum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Commitment Fee Percentage	0.13%
Line of Credit | Amended Credit Agreement 2012 | Maximum [Member]
Line of Credit Facility [Abstract]
Line of Credit Facility, Commitment Fee Percentage	0.30%
Line of Credit | Amended Credit Agreement 2012 | Federal Funds Effective Swap Rate
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	0.50%
Line of Credit | Amended Credit Agreement 2012 | Eurodollar
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	1.00%
Line of Credit | Amended Credit Agreement 2012 | Base Rate | Minimum [Member]
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	0.00%
Line of Credit | Amended Credit Agreement 2012 | Base Rate | Maximum [Member]
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	0.88%
Line of Credit | Amended Credit Agreement 2012 | London Interbank Offered Rate (LIBOR) | Minimum [Member]
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	1.00%
Line of Credit | Amended Credit Agreement 2012 | London Interbank Offered Rate (LIBOR) | Maximum [Member]
Line of Credit Facility [Abstract]
Debt Instrument, Basis Spread on Variable Rate	1.88%
Subordinated Debt
Debt Instruments [Abstract]
Maturity Date	31-Jul-24
Line of Credit Facility [Abstract]
Subordinated Loan Agreement Maximum Borrowing Capacity	300					300
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Minimum	5.75%
Debt Instrument, Interest Rate, Stated Percentage Rate Range, Maximum	9.75%
Subordinated Debt | Subordinated Loan Agreement with BPHC
Debt Instruments [Abstract]
Repayments of Subordinated Debt				100
Capital Lease Obligations
Debt Instruments [Abstract]
Capital Lease Obligations, Noncurrent	$9.60	$10				$9.60
[1]	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and repay all amounts outstanding under the subordinated loan agreement that was in place at that time, or $100.0 million.
[2]	The net proceeds of this offering were used to retire all of the outstanding Gulf South 2015 Notes and the remainder of the net proceeds was used to reduce outstanding borrowings under the Partnership’s revolving credit facility.
[3]	The net proceeds of this offering were used to reduce borrowings under the Partnership’s revolving credit facility and to redeem $225.0 million of Gulf South's 5.75% notes due August 2012 (2012 Notes) discussed below. BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.

Financing_Schedule_of_Capital_

Financing Schedule of Capital Units (Details) (USD $)	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012		Sep. 30, 2012		Mar. 31, 2012		Dec. 31, 2014	Dec. 31, 2013
Capital Unit [Line Items]
Percent of General Partner Interest Owned by Holding Company		2.00%						2.00%	2.00%
Common Units | Second Quarter 2013 Offering
Capital Unit [Line Items]
Month of Offering	29-May-13
Partners' Capital Account, Units, Sold in Public Offering	12.7
Issuance Price (in dollars per share)	$30.12
Less Underwriting Discounts and Expenses	$12.30
Proceeds from Issuance or Sale of Equity	376.5
Common Units Outstanding After Offering	220.3
Common Units Held by the Public After Offering	117.6
Percent of General Partner Interest Owned by Holding Company	2.00%
Common Units | Fourth Quarter 2012 Offering
Capital Unit [Line Items]
Month of Offering		5-Oct-12	[1]
Partners' Capital Account, Units, Sold in Public Offering		11.2
Issuance Price (in dollars per share)		$26.99
Less Underwriting Discounts and Expenses		10.4
Proceeds from Issuance or Sale of Equity		297.6
Common Units Outstanding After Offering		207.7
Common Units Held by the Public After Offering		105
Percent of General Partner Interest Owned by Holding Company		2.00%
Common Units | Third Quarter 2012 Offering
Capital Unit [Line Items]
Month of Offering				2-Aug-12	[1]
Partners' Capital Account, Units, Sold in Public Offering				11.6
Issuance Price (in dollars per share)				$27.80
Less Underwriting Discounts and Expenses				11.2
Proceeds from Issuance or Sale of Equity				317.9
Common Units Outstanding After Offering				196.5
Common Units Held by the Public After Offering				93.8
Percent of General Partner Interest Owned by Holding Company				2.00%
Common Units | First Quarter 2012 Offering
Capital Unit [Line Items]
Month of Offering						1-Feb-12	[1]
Partners' Capital Account, Units, Sold in Public Offering						9.2
Issuance Price (in dollars per share)						$27.55
Less Underwriting Discounts and Expenses						8.5
Proceeds from Issuance or Sale of Equity						$250.20
Common Units Outstanding After Offering						184.9
Common Units Held by the Public After Offering						82.2
Percent of General Partner Interest Owned by Holding Company						2.00%
[1]	BPHC waived the prepayment provisions under the then existing subordinated loan agreement that would have required a prepayment under such agreement as a result of this offering.

Financing_Summary_of_Changes_i

Financing Summary of Changes in Outstanding Units (Details) (USD $)	0 Months Ended		12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Oct. 09, 2013		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2014
Registration Rights Agreement [Abstract]
Number of common units registered for resale under Amended and Restated Registration Rights Agreement (in number of units)							27.9
Maximum amount Partnership must pay for reimbursement of underwriting discounts and commissions (in dollars per unit)							0.914
Accrued liability for future underwriting discounts and commissions			16				16
Statement [Line Items]
Conversion of Stock, Shares Converted (Class B)	22.9
Common Units
Statement [Line Items]
Balance, Beginning (in units)			207.7		175.7		243.3
Common units issued in connection with underwritten offerings			12.7		32
Conversion of Stock, Shares Converted (Class B)	22.9
Balance, Ending (in units)			243.3		207.7		243.3
Class B Units
Statement [Line Items]
Balance, Beginning (in units)			22.9	[1]	22.9	[1]	0	[1]
Common units issued in connection with underwritten offerings			0	[1]	0	[1]
Conversion of Stock, Shares Converted (Class B)	-22.9	[1]
Balance, Ending (in units)			0	[1]	22.9	[1]	0	[1]
[1]	On October 9, 2013, all of the 22.9 million class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.

Financing_Subsequent_Event_Det

Financing Subsequent Event (Details) (USD $)	12 Months Ended			0 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Feb. 02, 2015	Feb. 18, 2015
Subsequent Event [Line Items]
Repayments of Unsecured Debt	$0	$0	$525
Line of Credit
Subsequent Event [Line Items]
Line of Credit Facility, Amount Outstanding	120	175
Line of Credit | Subsequent Event
Subsequent Event [Line Items]
Line of Credit Facility, Amount Outstanding					460
Line of Credit Facility, Remaining Borrowing Capacity					540
Gulf South 5.05% Notes Due 2015 | Unsecured Debt | Subsequent Event
Subsequent Event [Line Items]
Repayments of Unsecured Debt				$275

Employee_Benefits_Details

Employee Benefits (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Defined Contribution Plan, Cost Recognized	$9	$8.60	$8
PBOP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution to defined benefit pension plan	0.1	0.1
Pension Plan
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Required amount of funding of periodic pension cost	3
Contribution to defined benefit pension plan	3	3
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year	3
Minimum amount of recognize expense each year associated with retirement plan	3
Future rate recovery	in excess of $6.0 million
Precluded future recovery of annual pension costs, lower range	3
Precluded future recovery of annual pension costs, upper range	6
Recognition of regulatory assets	in excess of $6.0 million
Reduction of regulatory assets	less than $3.0 million
Pension plan costs charged to expense, lower range	3
Pension plan costs charged to expense, upper range	6
SRP
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Contribution to defined benefit pension plan	$0	$0

Employee_Benefits_Projected_Be

Employee Benefits, Projected Benefit Obligation, Fair Value of Assets, Funded Status and the Amounts Not Yet Recognized As Components of Net Periodic Pension and Postretirement Benefits Cost (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Retirement Plans
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	$148.50	$152.50
Service cost	3.9	3.9	4
Interest cost	5.8	5	5.8
Plan participants’ contributions	0	0
Actuarial loss (gain)	3.6	-1.2
Benefits paid	-0.5	-0.4
Settlement	-11.4	-11.3
Benefit obligation at end of period	149.9	148.5	152.5
Change in Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	131.4	125.7
Actual return on plan assets	8.2	14.4
Benefits paid	-0.5	-0.4
Settlement	-11.4	-11.3
Company contributions	3	3
Plan participants’ contributions	0	0
Fair value of plan assets at end of period	130.7	131.4	125.7
Funded status	-19.2	-17.1
Items Not Recognized As Components Of Net Periodic Cost [Abstract]
Prior service cost (credit)	0	0
Net actuarial loss	26	24.4
Total	26	24.4
PBOP
Defined Benefit Plan, Change in Benefit Obligation [Roll Forward]
Benefit obligation at beginning of period	50	59.5
Service cost	0.4	0.5	0.5
Interest cost	2.2	2.1	2.4
Plan participants’ contributions	0.9	0.8
Actuarial loss (gain)	5.2	-8.3
Benefits paid	-3.6	-4.6
Settlement	0	0
Benefit obligation at end of period	55.1	50	59.5
Change in Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	80.8	86.7
Actual return on plan assets	9.1	-2.2
Benefits paid	-3.6	-4.6
Settlement	0	0
Company contributions	0.1	0.1
Plan participants’ contributions	0.9	0.8
Fair value of plan assets at end of period	87.3	80.8	86.7
Funded status	32.2	30.8
Items Not Recognized As Components Of Net Periodic Cost [Abstract]
Prior service cost (credit)	-8.6	-16.4
Net actuarial loss	10.7	10.6
Total	$2.10	($5.80)

Employee_Benefits_Aggregate_In

Employee Benefits, Aggregate Information Related Only to the Underfunded Plans (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013
In Millions, unless otherwise specified
Defined Benefit Plan Disclosure [Line Items]
Projected benefit obligation	$149.90	$148.50
Accumulated benefit obligation	139.7	138.4
Fair value of plan assets	$130.70	$131.40

Employee_Benefits_Components_o

Employee Benefits, Components of Net Periodic Benefit Cost (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Retirement Plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$3.90	$3.90	$4
Interest cost	5.8	5	5.8
Expected return on plan assets	-9.5	-9.1	-8.6
Amortization of prior service credit	0	0	0
Amortization of unrecognized net loss	1.4	2.1	2.1
Settlement charge	1.9	1.7	0
Net periodic benefit cost	3.5	3.6	3.3
PBOP
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	0.4	0.5	0.5
Interest cost	2.2	2.1	2.4
Expected return on plan assets	-4.2	-4.5	-4.3
Amortization of prior service credit	-7.8	-7.8	-7.8
Amortization of unrecognized net loss	0.3	0	0.1
Settlement charge	0	0	0
Net periodic benefit cost	($9.10)	($9.70)	($9.10)
Pension Plan
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Future rate recovery	in excess of $6.0 million

Employee_Benefits_Estimated_Fu

Employee Benefits, Estimated Future Benefit Payments (Details) (USD $)	Dec. 31, 2014
In Millions, unless otherwise specified
Retirement Plans
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2015	$16.30
2016	15
2017	14.8
2018	15
2019	15.7
2020-2024	67.1
PBOP
Defined Benefit Plan, Expected Future Benefit Payments, Fiscal Year Maturity [Abstract]
2015	3.1
2016	3.1
2017	3.2
2018	3.3
2019	3.3
2020-2024	$16.50

Employee_Benefits_WeightedAver

Employee Benefits, Weighted-Average Assumptions Used to Determine Benefit Obligations (Details)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (percent)	3.35%	4.00%
Expected return on plan assets (percent)	7.50%	7.50%	7.50%
Rate of compensation increase (percent)	3.50%	3.50%
SRP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (percent)	3.75%	4.25%
Expected return on plan assets (percent)	7.50%	7.50%	7.50%
Rate of compensation increase (percent)	3.50%	3.50%
PBOP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate (percent)	3.90%	4.50%
Expected return on plan assets (percent)	5.30%	5.30%	5.30%
Rate of compensation increase (percent)	0.00%	0.00%

Employee_Benefits_WeightedAver1

Employee Benefits, Weighted-Average Assumptions Used to Determine Net Periodic Benefit Cost (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2013		Sep. 30, 2013		Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plan
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)	4.10%	[1]	3.25%	[1]	4.00%		4.25%
Expected return on plan assets (percent)					7.50%	7.50%	7.50%
Rate of compensation increase (percent)					3.50%	3.50%	4.00%
SRP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)					4.25%	3.50%	4.25%
Expected return on plan assets (percent)					7.50%	7.50%	7.50%
Rate of compensation increase (percent)					3.50%	3.50%	4.00%
PBOP
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate (percent)					4.50%	3.90%	4.70%
Expected return on plan assets (percent)					5.30%	5.30%	5.30%
Rate of compensation increase (percent)					0.00%	0.00%	0.00%
[1]	Pension expense was remeasured at September 30, 2013, to reflect a settlement.

Employee_Benefits_Effect_of_On

Employee Benefits, Effect of One-Percentage-Point Change in Assumed Health Care Cost Trend Rates (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	5.00%	5.00%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	2022	2022
Annual increments for change	0.50%	0.50%
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	8.00%	8.50%
PBOP
Defined Benefit Plan, Effect of One-Percentage Point Change in Assumed Health Care Cost Trend Rates [Abstract]
Defined Benefit Plan, Effect of One Percentage Point Increase on Accumulated Postretirement Benefit Obligation	2.2
Defined Benefit Plan, Effect of One Percentage Point Increase on Service and Interest Cost Components	0.1
Defined Benefit Plan, Effect of One Percentage Point Decrease on Accumulated Postretirement Benefit Obligation	-1.9
Defined Benefit Plan, Effect of One Percentage Point Decrease on Service and Interest Cost Components	-0.1

Employee_Benefits_Master_Trust

Employee Benefits, Master Trust Pension and PBOP Fair Value Hierarchy (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plan
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	$256.20	$257.50
Master Trust percentage of pension plan assets	51.00%	51.00%
Amount committed to future capital calls in exchange for an ownership interest	8.1
Pension Plan | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	153.9	149.1
Pension Plan | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	62.7	67
Pension Plan | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	39.6	41.4
Pension Plan | Equity securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	42.3	44.6
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	40.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	60.00%
Pension Plan | Equity securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	42.3	44.6
Pension Plan | Equity securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Equity securities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Short-term investments
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	11.8	4.4
Pension Plan | Short-term investments | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	11.8	4.4
Pension Plan | Short-term investments | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Short-term investments | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Other assets
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1.1	3.4
Pension Plan | Other assets | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	1.1	0
Pension Plan | Other assets | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	3.4
Pension Plan | Other assets | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Fixed income mutual funds
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	98.7	100.4
Pension Plan | Fixed income mutual funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	98.7	100.1
Pension Plan | Fixed income mutual funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0.3
Pension Plan | Fixed income mutual funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Asset-backed securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	6	5.8
Pension Plan | Asset-backed securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Asset-backed securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	6	5.8
Pension Plan | Asset-backed securities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Hedge Funds
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	86.2	87.2
Pension Plan | Hedge Funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Hedge Funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	56.7	57.5
Pension Plan | Hedge Funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	29.5	29.7
Pension Plan | Private Equity Funds
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	10.1	11.7
Pension Plan | Private Equity Funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Private Equity Funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
Pension Plan | Private Equity Funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	10.1	11.7
Pension Plan | Alternative Investments
Defined Contribution Plan Disclosure [Line Items]
Defined Benefit Plan, Target Plan Asset Allocations Range Minimum	40.00%
Defined Benefit Plan, Target Plan Asset Allocations Range Maximum	60.00%
Retirement Plans
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	130.7	131.4	125.7
PBOP
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	87.3	80.8	86.7
Allocation to fixed income securities	100.00%	100.00%
PBOP | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	6.2	5.5
PBOP | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	81.1	75.3
PBOP | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Short-term investments
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	3.2	2.7
PBOP | Short-term investments | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	3.2	2.7
PBOP | Short-term investments | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Short-term investments | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Fixed income mutual funds
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	3	2.8
PBOP | Fixed income mutual funds | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	3	2.8
PBOP | Fixed income mutual funds | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Fixed income mutual funds | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Asset-backed securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	20.4	19.8
PBOP | Asset-backed securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Asset-backed securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	20.4	19.8
PBOP | Asset-backed securities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Corporate Bond Securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	17.8	16.9
PBOP | Corporate Bond Securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Corporate Bond Securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	17.8	16.9
PBOP | Corporate Bond Securities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Tax exempt securities
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	42.9	38.6
PBOP | Tax exempt securities | Fair Value, Inputs, Level 1 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	0	0
PBOP | Tax exempt securities | Fair Value, Inputs, Level 2 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	42.9	38.6
PBOP | Tax exempt securities | Fair Value, Inputs, Level 3 | Fair Value, Measurements, Recurring
Defined Contribution Plan Disclosure [Line Items]
Fair value of plan assets	$0	$0

Employee_Benefits_Fair_Value_M

Employee Benefits, Fair Value Measurement Using Significant Unobservable Inputs, Master Trust (Details) (Pension Plan, Fair Value, Inputs, Level 3, Fair Value, Measurements, Recurring, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Limited Partnership: Hedge funds
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	$29.70	$32
Actual return on assets still held	2.1	6.2
Actual return on assets sold	0.1	-0.3
Purchases, sales and settlements	-2.4	-8.2
Net transfers in/(out) of Level 3	0	0
Fair value of plan assets at end of period	29.5	29.7
Limited Partnership: Private equity
Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward]
Fair value of plan assets at beginning of period	11.7	7.1
Actual return on assets still held	0.2	2.1
Actual return on assets sold	0.8	-0.3
Purchases, sales and settlements	-2.6	2.8
Net transfers in/(out) of Level 3	0	0
Fair value of plan assets at end of period	$10.10	$11.70

Employee_Benefits_Summary_of_A

Employee Benefits, Summary of Activity in Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans (Details) (USD $)	0 Months Ended		12 Months Ended
In Millions, except Share data, unless otherwise specified	Feb. 07, 2013		Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
	Y		Y		Y		Y
LTIP | Phantom Share Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding balance, beginning (in units)			380,048	[1]	192,595	[1]
Granted (in units)					220,808
Paid (in units)			-171,411
Forfeited (in units)			-8,968		-33,355
Outstanding balance, ending (in units)			199,669	[1]	380,048	[1]	192,595	[1]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Fair Value [Abstract]
Outstanding balance, beginning			$10.90	[1]	$4.70	[1]
Granted					5.7
Paid			-3.5
Forfeited			0		0
Outstanding balance, ending			4.1	[1]	10.9	[1]	4.7	[1]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Weighted-Average Vesting Period [Abstract]
Outstanding balance, beginning (in years)			1.5	[1]	2	[1]
Granted (in years)					2.8
Outstanding balance, ending (in years)			0.9	[1]	1.5	[1]	2	[1]
Unit Appreciation Rights, Weighted-Average Exercise Price [Abstract]
Compensation expense			1.2		3.2		1.5
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			3,525,000
Share-based Compensation Arrangement by Share-based Payment Award, Shares Purchased for Award			16,064		7,484
Share-based Compensation Arrangement by Share-based Payment Award, Per Share Weighted Average Price of Shares Purchased			$12.51		$26.72
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			3,490,160
Closing market price of the common unit			$17.77		$25.52
Total estimated remaining unrecognized compensation expense related to the Phantom Common Units outstanding			1.6		6.1
Cash Bonus Plan
Unit Appreciation Rights, Weighted-Average Exercise Price [Abstract]
Cash Bonus Granted During Period			9.2
Compensation expense under cash bonus plan			2.6		0.5		0.6
Unrecognized compensation cost			6.6
Unit Appreciation Rights | Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding balance, beginning (in units)			479,008	[2]	605,747	[2]
Granted (in units)	293,809	[3]
Paid (in units)					-359,148
Vested (in units)			-203,168	[4]
Forfeited (in units)			-10,348		-61,400
Outstanding balance, ending (in units)			265,492	[2]	479,008	[2]	605,747	[2]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Fair Value [Abstract]
Outstanding balance, beginning			1.9	[2]	1.7	[2]
Granted	1.8	[3]
Outstanding balance, ending			0	[2]	1.9	[2]	1.7	[2]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Weighted-Average Vesting Period [Abstract]
Outstanding balance, beginning (in years)			1.5	[2]	1.4	[2]
Granted (in years)	2.8	[3]
Outstanding balance, ending (in years)			0.9	[2]	1.5	[2]	1.4	[2]
Unit Appreciation Rights, Weighted-Average Exercise Price [Abstract]
Outstanding balance, beginning (in dollars per unit)			$27.47	[2]	$29.18	[2]
Granted (in dollars per unit)	$27.57	[3]
Outstanding balance, ending (in dollars per unit)			$27.57	[2]	$27.47	[2]	$29.18	[2]
Compensation expense			-0.7		0.9		0.3
Unrecognized compensation cost			0		0.9
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value			0
SLTIP | Phantom Share Units (PSUs)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding balance, beginning (in units)			0		145	[1]
Paid (in units)					-145
Outstanding balance, ending (in units)			0		0		145	[1]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Fair Value [Abstract]
Outstanding balance, beginning			0		6.9	[1]
Paid					-7.2
Outstanding balance, ending			0		0		6.9	[1]
Unit Appreciation Rights and All Unit-Based Incentive Compensation Plans, Units, Weighted-Average Vesting Period [Abstract]
Outstanding balance, beginning (in years)			0		0.2	[1]
Outstanding balance, ending (in years)			0		0		0.2	[1]
Unit Appreciation Rights, Weighted-Average Exercise Price [Abstract]
Compensation expense			$0		$0.20		$2.30
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized			500
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant			0
[1]	Represents fair value and remaining weighted-average vesting period of outstanding awards at the end of the period.
[2]	Represents weighted-average exercise price, remaining weighted-average vesting period and total fair value of outstanding awards at the end of the period.
[3]	Represents the weighted-average exercise price and weighted-average vesting period of awards at grant date. The exercise price for each UAR granted was set at $27.57, the closing price of the Partnership’s common units on the New York Stock Exchange on the grant date on February 7, 2013.
[4]	Units vested and expired with no value.

Employee_Benefits_Valuation_As

Employee Benefits, Valuation Assumptions Under Unit Appreciation Rights (Details) (Unit Appreciation Rights, Stock Appreciation Rights (SARs))	12 Months Ended
	Dec. 31, 2013
Unit Appreciation Rights | Stock Appreciation Rights (SARs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	2 years 9 months 18 days
Risk Free Interest Rate (percent)	0.35%	[1]
Expected volatility (percent)	32.00%	[2]
[1]	Based on the U.S. Treasury yield curve corresponding to the remaining life of the UAR.
[2]	Based on the historical volatility of the Partnership’s common units.

Employee_Benefits_Employee_Ben

Employee Benefits Employee Benefits, Retention Payment Agreements (Details) (Retention Payment Agreements, USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014
Retention Payment Agreements
Deferred Compensation Arrangement with Individual, Excluding Share-based Payments and Postretirement Benefits [Line Items]
Deferred Compensation Arrangement with Individual, Cash Award Granted, Amount	$12
25% Vesting on February 28, 2015	25.00%
25% Vesting on February 29, 2016	25.00%
50% Vesting on February 28, 2017	50.00%
Deferred Compensation Arrangement with Individual, Compensation Expense	4.8
Unrecognized Compensation Cost for Retention Payments	$7

Cash_Distributions_and_Net_Inc2

Cash Distributions and Net Income per Unit (Details) (USD $)	0 Months Ended	9 Months Ended	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Oct. 09, 2013	Sep. 30, 2013	Dec. 31, 2014
Cash Distribution [Abstract]
Class B unitholders maximum quarterly distribution per unit (in dollars per unit)		$0.30
Conversion of Stock, Shares Converted (Class B)	22.9
First Target Distribution Range [Member]
Cash Distribution [Abstract]
Maximum target distribution amount (in dollars per share)			$0.40
Marginal Percentage Interest in Distributions - Limited Partner Unitholders			98.00%	[1]
Marginal Percentage Interest in Distributions - General Partner and IDRs Unitholders			2.00%
Second Target Distribution Range [Member] [Member]
Cash Distribution [Abstract]
Minimum target distribution amount (in dollars per share)			$0.40
Maximum target distribution amount (in dollars per share)			$0.44
Marginal Percentage Interest in Distributions - Limited Partner Unitholders			85.00%	[1]
Marginal Percentage Interest in Distributions - General Partner and IDRs Unitholders			15.00%
Third Target Distribution Range [Member]
Cash Distribution [Abstract]
Minimum target distribution amount (in dollars per share)			$0.44
Maximum target distribution amount (in dollars per share)			$0.53
Marginal Percentage Interest in Distributions - Limited Partner Unitholders			75.00%	[1]
Marginal Percentage Interest in Distributions - General Partner and IDRs Unitholders			25.00%
Thereafter Target Distribution Range [Member]
Cash Distribution [Abstract]
Minimum target distribution amount (in dollars per share)			$0.53
Marginal Percentage Interest in Distributions - Limited Partner Unitholders			50.00%	[1]
Marginal Percentage Interest in Distributions - General Partner and IDRs Unitholders			50.00%
[1]	The class B unitholders participated in distributions on a pari passu basis with the Partnership’s common units up to $0.30 per unit per quarter. The class B units did not participate in quarterly distributions above $0.30 per unit and converted into common units on a one-for-one basis on October 9, 2013.

Cash_Distributions_and_Net_Inc3

Cash Distributions and Net Income per Unit Distributions Made to Members or Limited Partners (Details) (USD $)	0 Months Ended	3 Months Ended
In Millions, except Per Share data, unless otherwise specified	Oct. 09, 2013	Dec. 31, 2014		Sep. 30, 2014		Jun. 30, 2014		Mar. 31, 2014		Dec. 31, 2013		Sep. 30, 2013		Jun. 30, 2013		Mar. 31, 2013		Dec. 31, 2012		Sep. 30, 2012		Jun. 30, 2012		Mar. 31, 2012
Distribution Made to Limited Partner [Line Items]
Payment Date		20-Nov-14		21-Aug-14		15-May-14		27-Feb-14		14-Nov-13		15-Aug-13		16-May-13		28-Feb-13		15-Nov-12		16-Aug-12		17-May-12		23-Feb-12
Distribution per Unit		$0.10		$0.10		$0.10		$0.10		$0.53		$0.53		$0.53		$0.53		$0.53		$0.53		$0.53		$0.53
Amount Paid to Common Unitholders		$24.30		$24.30		$24.30		$24.30		$129.50		$117.30		$110.60		$110.60		$110.60		$104.60		$98.50		$98.10
Amount Paid to Class B Unitholder		0		0		0		0		0	[1]	6.9		6.8		6.9		6.9		6.9		6.8		6.8
Amount Paid to General Partner (Including IDRs)		0.5	[2]	0.5	[2]	0.5	[2]	0.5	[2]	12.4	[2]	11.4	[2]	10.7	[2]	10.8	[2]	10.8	[2]	10.2	[2]	9.6	[2]	9.1	[2]
General partner interest (percent)		2.00%								2.00%								2.00%
Distributions paid on behalf of IDRs		$0								$34.60								$30.10
Conversion of Stock, Shares Converted (Class B)	22.9
[1]	On October 9, 2013, all of the 22.9 million Class B units were converted into common units on a one-for-one basis, pursuant to the terms of the partnership agreement.
[2]	In February 2014, the Partnership decreased its distribution rate to $0.10 per common unit. As a result of the reduced distribution rate, the quarterly target distribution levels for IDR payout were not met and the Partnership paid no amounts with respect to the IDRs in 2014. In 2013 and 2012, the Partnership paid $34.6 million and $30.1 million in distributions on behalf of IDRs.

Cash_Distributions_and_Net_Inc4

Cash Distributions and Net Income per Unit Reconciliation of Net Income and the Assumed Allocation of Net Income (Details) (USD $)	3 Months Ended								9 Months Ended	12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Reconciliation And Allocation of Net Income By Class of Stock [Line Items]
Class B unitholders' maximum quarterly distribution per unit									$0.30
Net income per unit [Abstract]
Net Income	$36.90	$28.40	$55.90	$25.60	$16.70	$61.70	$70.40	$101.40		$146.80	$250.20	$306
Net loss attributable to noncontrolling interests	0.1	-0.8	-1.5	-84.6	-2.8	-0.6	-0.1	0		-86.8	-3.5	0
Less: Net loss attributable to predecessor equity												-2.2
Net income attributable to controlling interests	36.8	29.2	57.4	110.2	19.5	62.3	70.5	101.4		233.6	253.7	306
Net Income Attributable To Limited Partner Unitholders And General Partner												308.2
Declared distribution										99.2	430.5	493.1
Assumed allocation of undistributed net income (loss)										134.4	-176.8	-184.9
Assumed allocation of net income attributable to limited partner unitholders and general partner										233.6	253.7	308.2
Allocation for diluted earnings per unit											0
Assumed allocation of net income attributable to limited partner unitholders and general partner - diluted											253.7
Common Units
Net income per unit [Abstract]
Declared distribution										97.2	381.8	424.3
Assumed allocation of undistributed net income (loss)										131.7	-160.5	-162
Assumed allocation of net income attributable to limited partner unitholders and general partner										228.9	221.3	262.3
Allocation for diluted earnings per unit											-4.6
Assumed allocation of net income attributable to limited partner unitholders and general partner - diluted											216.7
Weighted-average units outstanding										243.3	220.5	191.9
Weighted-average units outstanding - diluted											226.8
Net income per unit										$0.94	$1	$1.37
Diluted net income per unit:											$0.96
Class B Units
Net income per unit [Abstract]
Declared distribution											13.7	27.5
Assumed allocation of undistributed net income (loss)											-12.8	-19.2
Assumed allocation of net income attributable to limited partner unitholders and general partner											0.9	8.3
Allocation for diluted earnings per unit											4.6
Assumed allocation of net income attributable to limited partner unitholders and general partner - diluted											5.5
Weighted-average units outstanding											17.6	22.9
Weighted-average units outstanding - diluted											11.3
Net income per unit											$0.05	$0.36
Diluted net income per unit:											$0.48
General Partner And IDRS
Net income per unit [Abstract]
Declared distribution										2	35	41.3
Assumed allocation of undistributed net income (loss)										2.7	-3.5	-3.7
Assumed allocation of net income attributable to limited partner unitholders and general partner										4.7	31.5	37.6
Allocation for diluted earnings per unit											0
Assumed allocation of net income attributable to limited partner unitholders and general partner - diluted											$31.50

Cash_Distributions_and_Net_Inc5

Cash Distributions and Net Income per Unit Subsequent Event (Details) (Subsequent Event, USD $)	Feb. 09, 2015
Subsequent Event
Subsequent Event [Line Items]
Dividends Payable, Amount Per Share	$0.10

Income_Taxes_Details

Income Taxes (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Summary of the Provision for Income Taxes [Line Items]
Deferred Tax Assets, Net	$0				$0				$0	$0
State and Local Income Tax Expense (Benefit), Continuing Operations [Abstract]
State									0.3	0.4	-0.2
Total									0.3	0.4	-0.2
Deferred Income Tax Expense (Benefit), Continuing Operations [Abstract]
Deferred State and Local Income Tax Expense (Benefit)									0.1	0.1	0.7
Total									0.1	0.1	0.7
Income taxes	$0	$0.10	$0.10	$0.20	$0.20	$0	$0.10	$0.20	$0.40	$0.50	$0.50

Credit_Risk_Details

Credit Risk (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Concentration Risk [Line Items]
Operating revenues	$304.60	$278.90	$293.40	$356.90	$312.90	$275.50	$288.70	$328.50	$1,233.80	$1,205.60	$1,185
Gas Imbalances and Gas Loaned to Customers
Gas loaned to customers [Abstract]
Gas Balancing Volume Amount (in MMbtu)	10,000,000				19,600,000				10,000,000	19,600,000
Average Market Price Of Gas Assumed	3.36				4.17				3.36	4.17
Gas Imbalance To Subsidiaries Asset Liability	33.6				81.7				33.6	81.7
Natural Gas Liquids Balancing Volume (in MMbbls) (Less than)	100,000				0				100,000	0
Natural Gas Liquids Imbalance to Subsidiaries Asset Liability	0.6				0				0.6	0
Devon Gas Services, LP [Member]
Concentration Risk [Line Items]
Operating revenues									$120.50	$127.10	$133.30
Major customer revenue as a percentage of total revenue (in hundredths)									10.00%	11.00%	12.00%

Related_Party_Transactions_Det

Related Party Transactions (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Related Party Transaction [Line Items]
Related Party Transaction, Expenses from Transactions with Related Party	$8.80	$8.30	$8.30
Percent of General Partner Interest Owned by Holding Company	2.00%	2.00%	2.00%
Cash dividends paid to Parent Company	52	296.8	285.7
Investment in unconsolidated affiliates	0	78.6
Distribution from unconsolidated affiliates	11.1	0	0
Payments of Ordinary Dividends, Noncontrolling Interest	7.9	0	0
Boardwalk Pipelines Holding Company | Boardwalk Bluegrass and Boardwalk Moss Lake
Related Party Transaction [Line Items]
Investment in unconsolidated affiliates	8.2	90
Payments of Ordinary Dividends, Noncontrolling Interest	7.9
Boardwalk Pipeline Partners, LP | Boardwalk Bluegrass and Boardwalk Moss Lake
Related Party Transaction [Line Items]
Investment in unconsolidated affiliates	0.8	11.9
Distribution from unconsolidated affiliates	2.2
Subordinated Debt
Related Party Transaction [Line Items]
Subordinated Loan Agreement Maximum Borrowing Capacity	$300

Supplemental_Disclosure_of_Cas2

Supplemental Disclosure of Cash Flow Information (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash paid during the period for:
Interest (net of amount capitalized)	$153	$151	$169.80	[1]
Income taxes, net	0.1	0.3	0.2
Non-cash adjustments:
Accounts payable and PPE	36.9	38.1	37.9
Capital lease obligations incurred	0	10.5	0
Payments for (Proceeds from) Derivative Instrument, Financing Activities			$9.60
[1]	The 2012 period includes payments of $9.6 million related to the settlements of interest rate derivatives.

Selected_Quarterly_Financial_D2

Selected Quarterly Financial Data (Unaudited) (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, except Per Share data, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating revenues	$304.60	$278.90	$293.40	$356.90	$312.90	$275.50	$288.70	$328.50	$1,233.80	$1,205.60	$1,185
Operating expenses	224.1	210.4	196.9	204.3	254.4	172.3	177.6	186.8	835.7	791.1	711.2
Operating income	80.5	68.5	96.5	152.6	58.5	103.2	111.1	141.7	398.1	414.5	473.8
Interest expense, net	44.2	39.9	40	40.8	41.1	40.9	40.6	40.3
Other (income) expense	-0.6	0.1	0.5	86	0.5	0.6	0	-0.2
Income before income taxes	36.9	28.5	56	25.8	16.9	61.7	70.5	101.6	147.2	250.7	306.5
Income taxes	0	0.1	0.1	0.2	0.2	0	0.1	0.2	0.4	0.5	0.5
Net Income	36.9	28.4	55.9	25.6	16.7	61.7	70.4	101.4	146.8	250.2	306
Net earnings (loss) attributable to noncontrolling interests	0.1	-0.8	-1.5	-84.6	-2.8	-0.6	-0.1	0	-86.8	-3.5	0
Net income attributable to controlling interests	$36.80	$29.20	$57.40	$110.20	$19.50	$62.30	$70.50	$101.40	$233.60	$253.70	$306
Common Units
Basic net income per unit:
Basic net income per unit:	$0.15	$0.12	$0.23	$0.44	$0.08	$0.27	$0.28	$0.42
Diluted net income per unit:
Diluted net income per unit:					$0.08	$0.21	$0.28	$0.42	$0.94	$0.96	$1.37
Class B Units
Basic net income per unit:
Basic net income per unit:					($0.02)	($0.32)	$0.03	$0.19
Diluted net income per unit:
Diluted net income per unit:					$0	$0	$0.03	$0.19	$0	$0.48	$0.36

Guarantee_of_Securities_of_Sub2

Guarantee of Securities of Subsidiaries Balance Sheets (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
In Millions, unless otherwise specified
Condensed Financial Statements, Captions [Line Items]
Equity Restrictions	$0	$0
Other Restricted Assets	0	0
Cash and cash equivalents	6.6	28.5	3.9	21.9
Receivables	110.9	119.2
Receivables - affiliate	0	1.1
Gas and liquids stored underground	4.1	0.7
Prepayments	14.5	12.9
Advances to affiliates	0	0
Other current assets	13.5	14.7
Total current assets	149.6	177.1
Investment in consolidated subsidiaries	0	0
Property, plant and equipment, gross	9,355.60	8,723.30
Less—accumulated depreciation and amortization	1,766.40	1,489.20
Property, plant and equipment, net	7,589.20	7,234.10
Other noncurrent assets	468	424.7
Advances to affiliates – noncurrent	0	0
Investment in unconsolidated affiliates	0	78.6
Total other assets	468	503.3
Total Assets	8,206.80	7,914.50
Payables	62.1	70.8
Payable to affiliates	1.5	1.2
Advances from affiliates	0	0
Other current liabilities	156.6	164
Total current liabilities	220.2	236
Total long-term debt and capital lease obligation	3,689.70	3,424.40
Payable to affiliate - noncurrent	16	16
Advances from affiliates - noncurrent	0	0
Other noncurrent liabilities	178.6	174.7
Total other liabilities and deferred credits	194.6	190.7
Total partners’ capital	4,102.30	3,976.90
Noncontrolling interest	0	86.5
Total Equity	4,102.30	4,063.40	3,877.10	3,487
Total Liabilities and Equity	8,206.80	7,914.50
Reportable Legal Entities | Parent Guarantor
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0.5	0.2	0.1	0.5
Receivables	0	0
Receivables - affiliate	0	0.1
Gas and liquids stored underground	0	0
Prepayments	0.1	0.3
Advances to affiliates	0	0
Other current assets	0.5	0
Total current assets	1.1	0.6
Investment in consolidated subsidiaries	1,970.60	1,480.80
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	0.3
Advances to affiliates – noncurrent	2,148.30	2,512.10
Investment in unconsolidated affiliates		0
Total other assets	2,148.30	2,512.40
Total Assets	4,120	3,993.80
Payables	0.2	0.2
Payable to affiliates	1.5	0.7
Advances from affiliates	0	0
Other current liabilities	0	0
Total current liabilities	1.7	0.9
Total long-term debt and capital lease obligation	0	0
Payable to affiliate - noncurrent	16	16
Advances from affiliates - noncurrent	0	0
Other noncurrent liabilities	0	0
Total other liabilities and deferred credits	16	16
Total partners’ capital	4,102.30	3,976.90
Noncontrolling interest	0	0
Total Equity	4,102.30	3,976.90
Total Liabilities and Equity	4,120	3,993.80
Reportable Legal Entities | Subsidiary Issuer
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	1.8	9.2	1	10.7
Receivables	0	0
Receivables - affiliate	0	0.1
Gas and liquids stored underground	0	0
Prepayments	0	0
Advances to affiliates	6.3	0
Other current assets	0	0
Total current assets	8.1	9.3
Investment in consolidated subsidiaries	6,744.10	6,138.30
Property, plant and equipment, gross	0	0
Less—accumulated depreciation and amortization	0	0
Property, plant and equipment, net	0	0
Other noncurrent assets	3.4	3.7
Advances to affiliates – noncurrent	212	168.7
Investment in unconsolidated affiliates		0
Total other assets	215.4	172.4
Total Assets	6,967.60	6,320
Payables	0.1	0
Payable to affiliates	0	0
Advances from affiliates	106.2	194.4
Other current liabilities	21.4	19.7
Total current liabilities	127.7	214.1
Total long-term debt and capital lease obligation	1,724.50	1,379.90
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	3,144.80	3,245.20
Other noncurrent liabilities	0	0
Total other liabilities and deferred credits	3,144.80	3,245.20
Total partners’ capital	1,970.60	1,480.80
Noncontrolling interest	0	0
Total Equity	1,970.60	1,480.80
Total Liabilities and Equity	6,967.60	6,320
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	4.3	19.1	2.8	10.7
Receivables	110.9	119.2
Receivables - affiliate	9	14.3
Gas and liquids stored underground	4.1	0.7
Prepayments	14.4	12.6
Advances to affiliates	106.2	194.4
Other current assets	19.2	23.8
Total current assets	268.1	384.1
Investment in consolidated subsidiaries	0	0
Property, plant and equipment, gross	9,355	8,722.70
Less—accumulated depreciation and amortization	1,765.80	1,488.60
Property, plant and equipment, net	7,589.20	7,234.10
Other noncurrent assets	465.2	420.7
Advances to affiliates – noncurrent	996.5	733.1
Investment in unconsolidated affiliates		78.6
Total other assets	1,461.70	1,232.40
Total Assets	9,319	8,850.60
Payables	61.8	70.6
Payable to affiliates	9	13.9
Advances from affiliates	6.3	0
Other current liabilities	141.7	153.3
Total current liabilities	218.8	237.8
Total long-term debt and capital lease obligation	1,965.20	2,044.50
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	212	168.7
Other noncurrent liabilities	178.9	174.8
Total other liabilities and deferred credits	390.9	343.5
Total partners’ capital	6,744.10	6,138.30
Noncontrolling interest	0	86.5
Total Equity	6,744.10	6,224.80
Total Liabilities and Equity	9,319	8,850.60
Eliminations
Condensed Financial Statements, Captions [Line Items]
Cash and cash equivalents	0	0	0	0
Receivables	0	0
Receivables - affiliate	-9	-13.4
Gas and liquids stored underground	0	0
Prepayments	0	0
Advances to affiliates	-112.5	-194.4
Other current assets	-6.2	-9.1
Total current assets	-127.7	-216.9
Investment in consolidated subsidiaries	-8,714.70	-7,619.10
Property, plant and equipment, gross	0	0
Less—accumulated depreciation and amortization	0	0
Property, plant and equipment, net	0	0
Other noncurrent assets	-0.6	0
Advances to affiliates – noncurrent	-3,356.80	-3,413.90
Investment in unconsolidated affiliates		0
Total other assets	-3,357.40	-3,413.90
Total Assets	-12,199.80	-11,249.90
Payables	0	0
Payable to affiliates	-9	-13.4
Advances from affiliates	-112.5	-194.4
Other current liabilities	-6.5	-9
Total current liabilities	-128	-216.8
Total long-term debt and capital lease obligation	0	0
Payable to affiliate - noncurrent	0	0
Advances from affiliates - noncurrent	-3,356.80	-3,413.90
Other noncurrent liabilities	-0.3	-0.1
Total other liabilities and deferred credits	-3,357.10	-3,414
Total partners’ capital	-8,714.70	-7,619.10
Noncontrolling interest	0	0
Total Equity	-8,714.70	-7,619.10
Total Liabilities and Equity	($12,199.80)	($11,249.90)

Guarantee_of_Securities_of_Sub3

Guarantee of Securities of Subsidiaries Statements of Income (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Operating Revenues:
Transportation									$1,065.10	$1,028	$1,058.30
Parking and lending									23.3	23.9	28
Storage									89.5	110.9	84.7
Other									55.9	42.8	14
Total operating revenues	304.6	278.9	293.4	356.9	312.9	275.5	288.7	328.5	1,233.80	1,205.60	1,185
Operating Costs and Expenses:
Fuel and transportation									120.7	93.4	79.4
Operation and maintenance									198.8	186.5	167.2
Administrative and general									125	117.4	115.3
Other operating costs and expenses									391.2	393.8	349.3
Total operating costs and expenses	224.1	210.4	196.9	204.3	254.4	172.3	177.6	186.8	835.7	791.1	711.2
Operating (loss) income	80.5	68.5	96.5	152.6	58.5	103.2	111.1	141.7	398.1	414.5	473.8
Other Deductions (Income):
Interest expense									165.5	163.4	161.5
Interest (income) expense - affiliates, net									0	0	6.9
Interest income									-0.6	-0.5	-0.7
Equity in earnings of subsidiaries									0	0	0
Equity losses in unconsolidated affiliates	0	0	0	0	0	0	0	0	86.5	1.2	0
Miscellaneous other income									-0.5	-0.3	-0.4
Total other deductions									250.9	163.8	167.3
Income (loss) before income taxes	36.9	28.5	56	25.8	16.9	61.7	70.5	101.6	147.2	250.7	306.5
Income taxes	0	0.1	0.1	0.2	0.2	0	0.1	0.2	0.4	0.5	0.5
Net income (loss)	36.9	28.4	55.9	25.6	16.7	61.7	70.4	101.4	146.8	250.2	306
Net loss attributable to noncontrolling interests	0.1	-0.8	-1.5	-84.6	-2.8	-0.6	-0.1	0	-86.8	-3.5	0
Net income (loss) attributable to controlling interests	36.8	29.2	57.4	110.2	19.5	62.3	70.5	101.4	233.6	253.7	306
Reportable Legal Entities | Parent Guarantor
Operating Revenues:
Transportation									0	0	0
Parking and lending									0	0	0
Storage									0	0	0
Other									0	0	0
Total operating revenues									0	0	0
Operating Costs and Expenses:
Fuel and transportation									0	0	0
Operation and maintenance									0	0	0
Administrative and general									0.2	-0.1	0.5
Other operating costs and expenses									0.2	0.3	0.3
Total operating costs and expenses									0.4	0.2	0.8
Operating (loss) income									-0.4	-0.2	-0.8
Other Deductions (Income):
Interest expense									0	0	0
Interest (income) expense - affiliates, net									-30	-33.6	-35.6
Interest income									0	0	0
Equity in earnings of subsidiaries									-204	-220.3	-271.2
Equity losses in unconsolidated affiliates									0	0
Miscellaneous other income									0	0	0
Total other deductions									-234	-253.9	-306.8
Income (loss) before income taxes									233.6	253.7	306
Income taxes									0	0	0
Net income (loss)									233.6	253.7	306
Net loss attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to controlling interests									233.6	253.7	306
Reportable Legal Entities | Subsidiary Issuer
Operating Revenues:
Transportation									0	0	0
Parking and lending									0	0	0
Storage									0	0	0
Other									0	0	0
Total operating revenues									0	0	0
Operating Costs and Expenses:
Fuel and transportation									0	0	0
Operation and maintenance									0	0.3	0
Administrative and general									0	0.8	0
Other operating costs and expenses									0	0.1	0
Total operating costs and expenses									0	1.2	0
Operating (loss) income									0	-1.2	0
Other Deductions (Income):
Interest expense									76.5	72.7	63.1
Interest (income) expense - affiliates, net									41.2	41.3	52.9
Interest income									0	0	0
Equity in earnings of subsidiaries									-321.7	-335.5	-387.2
Equity losses in unconsolidated affiliates									0	0
Miscellaneous other income									0	0	0
Total other deductions									-204	-221.5	-271.2
Income (loss) before income taxes									204	220.3	271.2
Income taxes									0	0	0
Net income (loss)									204	220.3	271.2
Net loss attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to controlling interests									204	220.3	271.2
Reportable Legal Entities | Non-Guarantor Subsidiaries
Operating Revenues:
Transportation									1,157.90	1,116.40	1,147.50
Parking and lending									23.3	24	28.7
Storage									90.4	111	85.4
Other									55.9	42.8	14
Total operating revenues									1,327.50	1,294.20	1,275.60
Operating Costs and Expenses:
Fuel and transportation									214.4	182	170
Operation and maintenance									198.8	186.2	167.2
Administrative and general									124.8	116.7	114.8
Other operating costs and expenses									391	393.4	349
Total operating costs and expenses									929	878.3	801
Operating (loss) income									398.5	415.9	474.6
Other Deductions (Income):
Interest expense									89	90.7	98.4
Interest (income) expense - affiliates, net									-11.2	-7.7	-10.4
Interest income									-0.6	-0.5	-0.7
Equity in earnings of subsidiaries									0	0	0
Equity losses in unconsolidated affiliates									86.5	1.2
Miscellaneous other income									-0.5	-0.3	-0.4
Total other deductions									163.2	83.4	86.9
Income (loss) before income taxes									235.3	332.5	387.7
Income taxes									0.4	0.5	0.5
Net income (loss)									234.9	332	387.2
Net loss attributable to noncontrolling interests									-86.8	-3.5	0
Net income (loss) attributable to controlling interests									321.7	335.5	387.2
Eliminations
Operating Revenues:
Transportation									-92.8	-88.4	-89.2
Parking and lending									0	-0.1	-0.7
Storage									-0.9	-0.1	-0.7
Other									0	0	0
Total operating revenues									-93.7	-88.6	-90.6
Operating Costs and Expenses:
Fuel and transportation									-93.7	-88.6	-90.6
Operation and maintenance									0	0	0
Administrative and general									0	0	0
Other operating costs and expenses									0	0	0
Total operating costs and expenses									-93.7	-88.6	-90.6
Operating (loss) income									0	0	0
Other Deductions (Income):
Interest expense									0	0	0
Interest (income) expense - affiliates, net									0	0	0
Interest income									0	0	0
Equity in earnings of subsidiaries									525.7	555.8	658.4
Equity losses in unconsolidated affiliates									0	0
Miscellaneous other income									0	0	0
Total other deductions									525.7	555.8	658.4
Income (loss) before income taxes									-525.7	-555.8	-658.4
Income taxes									0	0	0
Net income (loss)									-525.7	-555.8	-658.4
Net loss attributable to noncontrolling interests									0	0	0
Net income (loss) attributable to controlling interests									($525.70)	($555.80)	($658.40)

Guarantee_of_Securities_of_Sub4

Guarantee of Securities of Subsidiaries Statements of Comprehensive Income (Details) (USD $)	3 Months Ended								12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net income (loss)	$36.90	$28.40	$55.90	$25.60	$16.70	$61.70	$70.40	$101.40	$146.80	$250.20	$306
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									-0.7	1.6	-7.1
Reclassification adjustment transferred to Net income from cash flow hedges									2.6	1.2	2
Pension and other postretirement benefit costs									-10.9	0.7	-12.8
Total Comprehensive Income (Loss)									137.8	253.7	288.1
Comprehensive loss attributable to noncontrolling interests									-86.8	-3.5	0
Comprehensive income (loss) attributable to controlling interests									224.6	257.2	288.1
Reportable Legal Entities | Parent Guarantor
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									233.6	253.7	306
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									-0.7	1.6	-7.1
Reclassification adjustment transferred to Net income from cash flow hedges									2.6	1.2	2
Pension and other postretirement benefit costs									-10.9	0.7	-12.8
Total Comprehensive Income (Loss)									224.6	257.2	288.1
Comprehensive loss attributable to noncontrolling interests									0	0	0
Comprehensive income (loss) attributable to controlling interests									224.6	257.2	288.1
Reportable Legal Entities | Subsidiary Issuer
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									204	220.3	271.2
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									-0.7	1.6	-7.1
Reclassification adjustment transferred to Net income from cash flow hedges									2.6	1.2	2
Pension and other postretirement benefit costs									-10.9	0.7	-12.8
Total Comprehensive Income (Loss)									195	223.8	253.3
Comprehensive loss attributable to noncontrolling interests									0	0	0
Comprehensive income (loss) attributable to controlling interests									195	223.8	253.3
Reportable Legal Entities | Non-Guarantor Subsidiaries
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									234.9	332	387.2
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									-0.7	1.6	-6.7
Reclassification adjustment transferred to Net income from cash flow hedges									0.9	-0.5	0.3
Pension and other postretirement benefit costs									-10.9	0.7	-12.8
Total Comprehensive Income (Loss)									224.2	333.8	368
Comprehensive loss attributable to noncontrolling interests									-86.8	-3.5	0
Comprehensive income (loss) attributable to controlling interests									311	337.3	368
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net income (loss)									-525.7	-555.8	-658.4
Other comprehensive income (loss):
(Loss) gain on cash flow hedges									1.4	-3.2	13.8
Reclassification adjustment transferred to Net income from cash flow hedges									-3.5	-0.7	-2.3
Pension and other postretirement benefit costs									21.8	-1.4	25.6
Total Comprehensive Income (Loss)									-506	-561.1	-621.3
Comprehensive loss attributable to noncontrolling interests									0	0	0
Comprehensive income (loss) attributable to controlling interests									($506)	($561.10)	($621.30)

Guarantee_of_Securities_of_Sub5

Guarantee of Securities of Subsidiaries Statements of Cash Flows (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	$513.60	$534.30	$575.50
INVESTING ACTIVITIES:
Capital expenditures	-404.4	-294.8	-226.9
Proceeds from sale of operating assets	2.9	60.7	5.9
Proceeds from insurance and other recoveries	6.3	1.4	10.4
Advances to affiliates, net	0.1	0	0
Investment in consolidated affiliates		0	0
Investment in unconsolidated affiliates	-20.5	-76.7	0
Distribution from unconsolidated affiliates	11.1	0	0
Acquisition of businesses, net of cash acquired	-294.7	0	-620.2
Net cash used in investing activities	-699.2	-309.4	-830.8
FINANCING ACTIVITIES:
Proceeds from long-term debt	342.9	0	818
Repayment of borrowings from long-term debt	0	0	-525
Proceeds from borrowings on revolving credit agreement	665	1,128	2,135
Repayment of borrowings on revolving credit agreement, including financing costs	-720	-1,255	-2,295.30
Repayment of borrowings from term loan	-25	0	0
Principal payment of capital lease obligation	-0.4	-0.2	0
Contribution from parent		0	0
Contribution received related to predecessor equity	0	0	269.2
Repayment of contribution received related to predecessor equity	0	0	-554
Advances from affiliates, net	0.1	-2.8	2.6
Distributions paid	-99.2	-533.9	-478.9
Capital contributions from noncontrolling interests	8.2	87.1	0
Distributions paid to noncontrolling interests	-7.9	0	0
Proceeds from sale of common units	0	368.7	847.7
Capital contribution from general partner	0	7.8	18
Net cash provided (used in) by financing activities	163.7	-200.3	237.3
(Decrease) increase in cash and cash equivalents	-21.9	24.6	-18
Cash and cash equivalents at beginning of period	28.5	3.9	21.9
Cash and cash equivalents at end of period	6.6	28.5	3.9
Eliminations
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	0	0	-689.5
INVESTING ACTIVITIES:
Capital expenditures	0	0	0
Proceeds from sale of operating assets	0	0	0
Proceeds from insurance and other recoveries	0	0	0
Advances to affiliates, net	-139	300.7	422.4
Investment in consolidated affiliates		15.1	415
Investment in unconsolidated affiliates	0	0
Distribution from unconsolidated affiliates	0
Acquisition of businesses, net of cash acquired	0		0
Net cash used in investing activities	-139	315.8	837.4
FINANCING ACTIVITIES:
Proceeds from long-term debt	0		0
Repayment of borrowings from long-term debt			0
Proceeds from borrowings on revolving credit agreement	0	0	0
Repayment of borrowings on revolving credit agreement, including financing costs	0	0	0
Repayment of borrowings from term loan	0
Principal payment of capital lease obligation	0	0
Contribution from parent		-15.1	-415
Contribution received related to predecessor equity			0
Repayment of contribution received related to predecessor equity			0
Advances from affiliates, net	139	-300.7	-422.4
Distributions paid	0	0	689.5
Capital contributions from noncontrolling interests	0	0
Distributions paid to noncontrolling interests	0
Proceeds from sale of common units		0	0
Capital contribution from general partner		0	0
Net cash provided (used in) by financing activities	139	-315.8	-147.9
(Decrease) increase in cash and cash equivalents	0	0	0
Cash and cash equivalents at beginning of period	0	0	0
Cash and cash equivalents at end of period	0	0	0
Parent Guarantor | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	30.2	33.9	31.4
INVESTING ACTIVITIES:
Capital expenditures	0	0	0
Proceeds from sale of operating assets	0	0	0
Proceeds from insurance and other recoveries	0	0	0
Advances to affiliates, net	363.9	126.4	-404.2
Investment in consolidated affiliates		0	-17
Investment in unconsolidated affiliates	0	0
Distribution from unconsolidated affiliates	0
Acquisition of businesses, net of cash acquired	-294.7		0
Net cash used in investing activities	69.2	126.4	-421.2
FINANCING ACTIVITIES:
Proceeds from long-term debt	0		0
Repayment of borrowings from long-term debt			0
Proceeds from borrowings on revolving credit agreement	0	0	0
Repayment of borrowings on revolving credit agreement, including financing costs	0	0	0
Repayment of borrowings from term loan	0
Principal payment of capital lease obligation	0	0
Contribution from parent		0	0
Contribution received related to predecessor equity			0
Repayment of contribution received related to predecessor equity			0
Advances from affiliates, net	0.1	-2.8	2.6
Distributions paid	-99.2	-533.9	-478.9
Capital contributions from noncontrolling interests	0	0
Distributions paid to noncontrolling interests	0
Proceeds from sale of common units		368.7	847.7
Capital contribution from general partner		7.8	18
Net cash provided (used in) by financing activities	-99.1	-160.2	389.4
(Decrease) increase in cash and cash equivalents	0.3	0.1	-0.4
Cash and cash equivalents at beginning of period	0.2	0.1	0.5
Cash and cash equivalents at end of period	0.5	0.2	0.1
Subsidiary Issuer | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	-112.1	-108.8	577.9
INVESTING ACTIVITIES:
Capital expenditures	0	0	0
Proceeds from sale of operating assets	0	0	0
Proceeds from insurance and other recoveries	0	0	0
Advances to affiliates, net	-49.6	-84.3	-84.4
Investment in consolidated affiliates		-15.1	-398
Investment in unconsolidated affiliates	0	0
Distribution from unconsolidated affiliates	0
Acquisition of businesses, net of cash acquired	0		0
Net cash used in investing activities	-49.6	-99.4	-482.4
FINANCING ACTIVITIES:
Proceeds from long-term debt	342.9		297.6
Repayment of borrowings from long-term debt			-100
Proceeds from borrowings on revolving credit agreement	0	0	300
Repayment of borrowings on revolving credit agreement, including financing costs	0	0	-403.8
Repayment of borrowings from term loan	0
Principal payment of capital lease obligation	0	0
Contribution from parent		0	17
Contribution received related to predecessor equity			0
Repayment of contribution received related to predecessor equity			-554
Advances from affiliates, net	-188.6	216.4	338
Distributions paid	0	0	0
Capital contributions from noncontrolling interests	0	0
Distributions paid to noncontrolling interests	0
Proceeds from sale of common units		0	0
Capital contribution from general partner		0	0
Net cash provided (used in) by financing activities	154.3	216.4	-105.2
(Decrease) increase in cash and cash equivalents	-7.4	8.2	-9.7
Cash and cash equivalents at beginning of period	9.2	1	10.7
Cash and cash equivalents at end of period	1.8	9.2	1
Non-Guarantor Subsidiaries | Reportable Legal Entities
Condensed Financial Statements, Captions [Line Items]
Net Cash Provided by (Used in) Operating Activities	595.5	609.2	655.7
INVESTING ACTIVITIES:
Capital expenditures	-404.4	-294.8	-226.9
Proceeds from sale of operating assets	2.9	60.7	5.9
Proceeds from insurance and other recoveries	6.3	1.4	10.4
Advances to affiliates, net	-175.2	-342.8	66.2
Investment in consolidated affiliates		0	0
Investment in unconsolidated affiliates	-20.5	-76.7
Distribution from unconsolidated affiliates	11.1
Acquisition of businesses, net of cash acquired	0		-620.2
Net cash used in investing activities	-579.8	-652.2	-764.6
FINANCING ACTIVITIES:
Proceeds from long-term debt	0		520.4
Repayment of borrowings from long-term debt			-425
Proceeds from borrowings on revolving credit agreement	665	1,128	1,835
Repayment of borrowings on revolving credit agreement, including financing costs	-720	-1,255	-1,891.50
Repayment of borrowings from term loan	-25
Principal payment of capital lease obligation	-0.4	-0.2
Contribution from parent		15.1	398
Contribution received related to predecessor equity			269.2
Repayment of contribution received related to predecessor equity			0
Advances from affiliates, net	49.6	84.3	84.4
Distributions paid	0	0	-689.5
Capital contributions from noncontrolling interests	8.2	87.1
Distributions paid to noncontrolling interests	-7.9
Proceeds from sale of common units		0	0
Capital contribution from general partner		0	0
Net cash provided (used in) by financing activities	-30.5	59.3	101
(Decrease) increase in cash and cash equivalents	-14.8	16.3	-7.9
Cash and cash equivalents at beginning of period	19.1	2.8	10.7
Cash and cash equivalents at end of period	$4.30	$19.10	$2.80

Schedule_II_Valuation_and_Qual1

Schedule II Valuation and Qualifying Accounts (Details) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$0	$0.20	$0.20
Additions:
Charged to Costs and Expenses	0	-0.2	0
Other Additions	0	0	0
Deductions	0	0	0
Balance at End of Period	$0	$0	$0.20