Columbia Pipeline Partners (CPPL) 10-Q 3 May 16 2016 Q1 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	3 Months Ended
	Mar. 31, 2016	Apr. 29, 2016
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	Q1
Entity Registrant Name	COLUMBIA PIPELINE PARTNERS LP/DE
Entity Central Index Key	1,420,783
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Common Units
Document Information [Line Items]
Entity Units Outstanding		53,834,784
Subordinated Units
Document Information [Line Items]
Entity Units Outstanding		46,811,398

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Millions		Mar. 31, 2016	Dec. 31, 2015
Current Assets
Cash and cash equivalents		$ 34.2	$ 78.9
Accounts receivable (less reserve of $0.3 and $0.3, respectively)		154.1	145.9
Accounts receivable-affiliated		122.6	149.4
Materials and supplies, at average cost		33.2	32.8
Exchange gas receivable		11.8	18.8
Deferred property taxes		54.2	52
Prepayments and other		31	33.8
Total Current Assets		441.1	511.6
Investments
Unconsolidated affiliates		436.2	437.1
Other investments		1.8	1.8
Total Investments		438	438.9
Property, Plant and Equipment
Property, plant and equipment		9,297.6	8,930.9
Accumulated depreciation and amortization		(2,994)	(2,960.1)
Net Property, Plant and Equipment		6,303.6	5,970.8
Other Noncurrent Assets
Regulatory assets		132.6	134.1
Goodwill		1,975.5	1,975.5
Postretirement and postemployment benefits assets		122.3	120.5
Deferred charges and other		10.9	10.6
Total Other Noncurrent Assets		2,241.3	2,240.7
Total Assets		9,424	9,162
Current Liabilities
Short-term borrowings		15	15
Short-term borrowings-affiliated		348.8	42.1
Accounts payable		46.2	49.9
Accounts payable-affiliated		22.6	86.3
Customer deposits		18.7	17.8
Taxes accrued		103.6	108.2
Exchange gas payable		11.7	18.2
Deferred revenue		10.5	15
Accrued capital expenditures		88	95.9
Accrued compensation and related costs		21.5	26.6
Other accruals		56.9	43.8
Total Current Liabilities		743.5	518.8
Noncurrent Liabilities
Long-term debt-affiliated		630.9	630.9
Deferred income taxes		1	1
Accrued liability for postretirement and postemployment benefits		35.8	36.1
Regulatory liabilities		291.9	309.7
Asset retirement obligations		24.7	25.3
Other noncurrent liabilities		65.8	63.5
Total Noncurrent Liabilities		1,050.1	1,066.5
Total Liabilities		1,793.6	1,585.3
Equity and Partners' Capital
Accumulated other comprehensive loss	[1]	(3.9)	(4)
Total Columbia Pipeline Partners LP partners' equity and capital		1,267.8	1,258.5
Noncontrolling Interest in Columbia OpCo		6,362.6	6,318.2
Total Equity and Partners' Capital		7,630.4	7,576.7
Total Liabilities and Equity and Partners' Capital		9,424	9,162
Common Units
Equity and Partners' Capital
Limited Partners' Capital Account		963.4	958.5
Subordinated Units
Equity and Partners' Capital
Limited Partners' Capital Account		$ 308.3	$ 304
[1]	Amounts in parentheses indicate debits.

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Accounts receivable less reserve	$ 0.3	$ 0.3
Common Units
Limited Partners' Capital Account, Units Issued	53,834,784	53,834,784
Limited Partners' Capital Account, Units Outstanding	53,834,784	53,834,784
Subordinated Units
Limited Partners' Capital Account, Units Issued	46,811,398	46,811,398
Limited Partners' Capital Account, Units Outstanding	46,811,398	46,811,398

Statements Of Consolidated and

Statements Of Consolidated and Combined Operations - USD ($) shares in Millions, $ in Millions	2 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Operating Revenues
Transportation revenues		$ 307.8	$ 247.9
Transportation revenues-affiliated		0	28.7
Storage revenues		49.9	36.6
Storage revenues-affiliated		0	13.3
Other revenues		5.8	12.7
Total Operating Revenues		363.5	339.2
Operating Expenses
Operation and maintenance		99.2	110
Operation and maintenance-affiliated		42.4	36.1
Depreciation and amortization		37.6	32.3
Gain on sale of assets		(2.6)	(5.3)
Property and other taxes		20.8	19
Total Operating Expenses		197.4	192.1
Equity Earnings in Unconsolidated Affiliates		15.8	14.9
Operating Income		181.9	162
Other Income (Deductions)
Interest expense		(0.6)	0
Interest expense-affiliated		(7.2)	(11.4)
Other, net		6.1	4.3
Total Other Deductions, net		(1.7)	(7.1)
Income before Income Taxes		180.2	154.9
Income Taxes		0	23.7
Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 88.5	180.2	131.2
Net Income	88.5	180.2	$ 131.2
Income (Loss) Attributable to Noncontrolling Interest	75.2	152.9
Net Income (Loss) Allocated to Limited Partners	$ 13.3	$ 27.3
Net income attributable to partners' ownership interest subsequent to IPO per limited partner unit (basic and diluted)
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13	$ 0.25
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	100.6	100.6
Common Units
Other Income (Deductions)
Net Income (Loss) Allocated to Limited Partners	$ 7.1	$ 13.4
Net income attributable to partners' ownership interest subsequent to IPO per limited partner unit (basic and diluted)
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13	$ 0.25
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	53.8	53.8
Subordinated Units
Other Income (Deductions)
Net Income (Loss) Allocated to Limited Partners	$ 6.2	$ 11.6
Net income attributable to partners' ownership interest subsequent to IPO per limited partner unit (basic and diluted)
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13	$ 0.25
Weighted average limited partner units outstanding (basic and diluted)
Weighted Average Number of Shares Outstanding, Basic and Diluted	46.8	46.8
Parent | Predecessor
Other Income (Deductions)
Income (Loss), Including Portion Attributable to Noncontrolling Interest	$ 0
Net Income	$ 0

Statements of Consolidated and5

Statements of Consolidated and Combined Comprehensive Income - USD ($) $ in Millions		1 Months Ended	2 Months Ended	3 Months Ended
		Feb. 11, 2015	Mar. 31, 2015	Mar. 31, 2016		Mar. 31, 2015
Net Income		$ 42.7	$ 88.5	$ 180.2		$ 131.2
Net unrealized gain on cash flow hedges	[1]			0.5		0.2
Other Comprehensive Income, Net of Tax and Transaction Adjustments				0.5		0.2
Total other comprehensive income		0.1	0.1	0.5	[2]	0.1	[3]
Total comprehensive income subsequent to IPO		$ 42.8	$ 88.6	180.7		131.4
Less: Comprehensive income attributable to noncontrolling interest subsequent to IPO				153.3		75.3
Comprehensive income attributable to limited partners subsequent to IPO				$ 27.4		$ 13.3
[1]	Net unrealized gains on derivatives qualifying as cash flow hedges, net of zero and $0.1 million tax expense for the three months ended March 31, 2016 and 2015, respectively
[2]	Amounts in parentheses indicate debits.
[3]	All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits.

Statements of Consolidated and6

Statements of Consolidated and Combined Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	$ 0	$ 0.1

Statements Of Consolidated and7

Statements Of Consolidated and Combined Cash Flows - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Operating Activities
Net Income	$ 180.2	$ 131.2
Adjustments to Reconcile Net Income to Net Cash from Operating Activities:
Depreciation and amortization	37.6	32.3
Deferred income taxes and investment tax credits	0	10.5
Deferred revenue	(2)	5.3
Equity-based compensation expense and profit sharing contribution	0.7	2
Gain on sale of assets	(2.6)	(5.3)
Equity earnings in unconsolidated affiliates	(15.8)	(14.9)
Amortization of debt related costs	0.1	0.1
AFUDC equity	(6.1)	(3.5)
Distributions of earnings received from equity investees	18.9	18.3
Changes in Assets and Liabilities:
Accounts receivable	(5.7)	12.2
Accounts receivable-affiliated	1.8	15.1
Accounts payable	(11.3)	(15.6)
Accounts payable-affiliated	(65.7)	(15.1)
Customer deposits	0.9	0.6
Taxes accrued	(4.7)	2.4
Exchange gas receivable/payable	0.6	0
Other accruals	(5.3)	(7.8)
Prepayments and other current assets	8.1	2.9
Regulatory assets/liabilities	1.4	11.8
Postretirement and postemployment benefits	(0.1)	(7.7)
Deferred charges and other noncurrent assets	(2.1)	(1.9)
Other noncurrent liabilities	3	0.8
Net Cash Flows from Operating Activities	131.9	173.7
Investing Activities
Capital expenditures	(377.4)	(163.9)
Change in short-term lendings-affiliated	24.9	(699.6)
Proceeds from disposition of assets	0	10.2
Contributions to equity investees	(1.9)	0
Distributions from equity investees	0.2	1.3
Other investing activities	(2)	(2.5)
Net Cash Flows used for Investing Activities	(356.2)	(854.5)
Financing Activities
Change in short-term borrowings-affiliated	306.6	(240.4)
Payments of long-term debt-affiliated, including current portion	0	(957.8)
Proceeds from the issuance of common units, net of offering costs	0	1,168.4
Distribution of IPO proceeds to parent	0	(500)
Contribution of capital from parent	0	1,217.3
Quarterly distributions to unitholders	(18.1)	0
Distribution to noncontrolling interest in Columbia OpCo	(108.9)	0
Net Cash Flows from Financing Activities	179.6	687.5
Change in cash and cash equivalents	(44.7)	6.7
Cash and cash equivalents at beginning of period	78.9	0.5
Cash and Cash Equivalents at End of Period	$ 34.2	$ 7.2

Statements Of Consolidated and8

Statements Of Consolidated and Combined Equity and Partners' Capital - USD ($) $ in Millions		Total		Parent	Noncontrolling Interest	Accumulated Other Comprehensive Loss	Limited PartnerCommon Units	Limited PartnerSubordinated Units
Beginning Balance (Predecessor) at Dec. 31, 2014				$ 4,188
Beginning Balance at Dec. 31, 2014		$ 4,171.3			$ 0	$ (16.7)	$ 0	$ 0
Income (Loss), Including Portion Attributable to Noncontrolling Interest | Predecessor				42.7
Income (Loss), Including Portion Attributable to Noncontrolling Interest		42.7			0	0	0	0
Other Comprehensive Income (Loss), Net of Tax | Predecessor				0
Other Comprehensive Income (Loss), Net of Tax		0.1			0	0.1	0	0
Contribution of capital from parent | Predecessor				1,217.3
Contribution of capital from parent		1,217.3			0	0	0	0
Predecessor net tax liabilities not assumed by Columbia OpCo | Predecessor				1,232.5
Predecessor net tax liabilities not assumed by Columbia OpCo		1,222.2			0	(10.3)	0	0
Contributed/Noncontributed Net Parent Investment Adjustments | Predecessor				(7.7)
Contributed/Noncontributed Net Parent Investment Adjustments		(7.7)			0	0	0	0
Ending Balance (Predecessor) at Feb. 11, 2015				6,672.8
Ending Balance at Feb. 11, 2015		6,645.9			0	(26.9)	0	0
Beginning Balance (Predecessor) at Dec. 31, 2014				4,188
Beginning Balance at Dec. 31, 2014		4,171.3			0	(16.7)	0	0
Income (Loss), Including Portion Attributable to Noncontrolling Interest		131.2
Other Comprehensive Income (Loss), Net of Tax	[1]	0.1
Predecessor net tax liabilities not assumed by Columbia OpCo	[1],[2]					(10.3)
Ending Balance at Mar. 31, 2015		7,402.9		0	6,162.7	(4.2)	948.4	296
Beginning Balance (Predecessor) at Feb. 11, 2015				6,672.8
Beginning Balance at Feb. 11, 2015		6,645.9			0	(26.9)	0	0
Income (Loss), Including Portion Attributable to Noncontrolling Interest | Predecessor				0
Income (Loss), Including Portion Attributable to Noncontrolling Interest		88.5			75.2	0	7.1	6.2
Other Comprehensive Income (Loss), Net of Tax | Predecessor				0
Other Comprehensive Income (Loss), Net of Tax		0.1			0.1	0	0	0
Allocation of Net Investment to Unitholders | Predecessor				(6,672.8)
Allocation of Net Investment to Unitholders		0			6,185.7	0	0	487.1
Allocation of Accumulated Other Comprehensive Loss to Noncontrolling Interest | Predecessor				0
Allocation of Accumulated Other Comprehensive Loss to Noncontrolling Interest		0			(22.7)	22.7	0	0
Net proceeds from IPO | Predecessor				0
Net proceeds from IPO		1,168.4			0	0	1,168.4	0
Purchase of additional interest in Columbia OpCo | Predecessor				0
Purchase of additional interest in Columbia OpCo		0			424.4	0	(227.1)	(197.3)
Distributions to the noncontrolling interest in Columbia OpCo | Predecessor				0
Distributions to the noncontrolling interest in Columbia OpCo		(500)			(500)	0	0	0
Ending Balance at Mar. 31, 2015		7,402.9		$ 0	6,162.7	(4.2)	948.4	296
Beginning Balance at Dec. 31, 2015		7,576.7			6,318.2	(4)	958.5	304
Income (Loss), Including Portion Attributable to Noncontrolling Interest		180.2			152.9	0	14.6	12.7
Other Comprehensive Income (Loss), Net of Tax		0.5	[3]		0.4	0.1	0	0
Quarterly distributions to unitholders		(18.1)			0	0	(9.7)	(8.4)
Purchase of additional interest in Columbia OpCo					0
Distributions to the noncontrolling interest in Columbia OpCo		(108.9)			(108.9)	0	0	0
Ending Balance at Mar. 31, 2016		$ 7,630.4			$ 6,362.6	$ (3.9)	$ 963.4	$ 308.3
[1]	All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits.
[2]	Reflects the non-cash elimination of all historical current and deferred income taxes other than Tennessee state income taxes that will continue to be borne by the Partnership post-IPO.
[3]	Amounts in parentheses indicate debits.

Statements of Consolidated and9

Statements of Consolidated and Combined Equity and Partners' Capital (Parenthetical) $ in Millions	2 Months Ended
	Mar. 31, 2015USD ($)
Net proceeds from IPO	$ 1,168.4
Common Units | Limited Partner
Net proceeds from IPO	$ 1,168.4
Columbia OpCo
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Additional Ownership Interest	8.40%
Hardy Storage
Equity Method Investment, Percent Not Contributed to Partnership	1.00%
Hardy Storage | Predecessor
Equity Method Investment, Ownership Percentage	50.00%

Basis of Accounting Presentatio

Basis of Accounting Presentation	3 Months Ended
	Mar. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting Presentation	Basis of Accounting Presentation Columbia Pipeline Partners LP (the "Partnership") was formed in Delaware on December 5, 2007 as a subsidiary of NiSource Inc. ("NiSource"). CEG owns the general partner of the Partnership and all of the Partnership’s subordinated units and incentive distribution rights. On February 11, 2015, NiSource contributed its subsidiary CEG to CPG. Following this contribution, CPG owns and operates, through its subsidiaries, approximately 15,000 miles of strategically located interstate gas pipelines extending from New York to the Gulf of Mexico and one of the nation’s largest underground natural gas storage systems, with approximately 300 MMDth of working gas capacity, as well as related gathering and processing assets. CEG owns and operates, through its subsidiaries, substantially all of the natural gas transmission and storage assets of CPG. Prior to July 1, 2015, CPG was a wholly owned subsidiary of NiSource. On July 1, 2015, all the shares of CPG were distributed by NiSource to holders of NiSource common stock completing CPG's separation from NiSource (the "Separation"). As a result of the Separation, CPG became an independent publicly traded company. Columbia Pipeline Partners LP Predecessor (the “Predecessor”) is comprised of NiSource’s Columbia Pipeline Group Operations reportable segment. The Partnership is engaged in regulated interstate gas transportation and storage services for LDCs, marketers, producers and industrial and commercial customers located in northeastern, mid-Atlantic, midwestern and southern states and the District of Columbia along with unregulated businesses that include midstream services, including gathering, treating, conditioning, processing, compression and liquids handling, and development of mineral rights positions. The regulated services are performed under tariffs at rates subject to FERC approval. Concurrent with the completed IPO, refer to Note 2 for a discussion of IPO results, NiSource contributed substantially all of the assets and operations of the Predecessor to Columbia OpCo, a Delaware limited partnership formed by CEG, which, prior to the Separation, was a wholly owned subsidiary of NiSource, and OpCo GP, a wholly owned subsidiary of the Partnership. The contribution is considered to be a reorganization of entities under common control. Subsequent to the IPO, the Partnership owns a 15.7% limited partner interest in Columbia OpCo and CEG owns the remaining 84.3% limited partner interest. MLP GP, a wholly owned subsidiary of CEG, serves as the general partner of the Partnership. OpCo GP serves as the general partner of Columbia OpCo. CPGSC provides services to the Partnership pursuant to an omnibus agreement. MLP GP, the Partnership, Columbia OpCo and OpCo GP have all adopted a fiscal year end of December 31. Through ownership of Columbia OpCo’s general partner, the Partnership controls all of Columbia OpCo’s assets and operations. As a result, the Partnership consolidates Columbia OpCo and CEG's retained interest of 84.3% is recorded as noncontrolling interest in the Partnership's consolidated financial statements. For periods subsequent to the closing of the IPO, the financial statements included in this quarterly report are the financial statements and accounting records of the Partnership. For periods prior to the closing of the IPO, the financial statements included in this quarterly report are the financial statements and accounting records of the Predecessor. The consolidated and combined financial statements were prepared as follows: • The Condensed Consolidated Balance Sheets (unaudited) consist of the consolidated balance sheets of the Partnership as of March 31, 2016 and December 31, 2015 . • The Condensed Statements of Consolidated and Combined Operations (unaudited) consist of consolidated results of the Partnership for the three months ended March 31, 2016 and for the period from February 11, 2015 through March 31, 2015 and the combined results of the Predecessor for the period from January 1, 2015 through February 10, 2015. • The Condensed Statements of Consolidated and Combined Comprehensive Income (unaudited) consist of consolidated results of the Partnership for the three months ended March 31, 2016 and for the period from February 11, 2015 through March 31, 2015 and the combined results of the Predecessor for the period from January 1, 2015 through February 10, 2015. • The Condensed Statements of Consolidated and Combined Cash Flows (unaudited) consist of consolidated cash flows of the Partnership for the three months ended March 31, 2016 and for the period from February 11, 2015 through March 31, 2015 and the combined cash flows of the Predecessor for the period from January 1, 2015 through February 10, 2015. • The Condensed Statements of Consolidated and Combined Equity and Partners' Capital (unaudited) consist of consolidated activity of the Partnership for the three months ended March 31, 2016 and for the period from February 11, 2015 through March 31, 2015 and the combined activity of the Predecessor for the period from January 1, 2015 through February 10, 2015. Merger. On March 17, 2016, CPG entered into an Agreement and Plan of Merger (the “Merger Agreement”), among CPG, TransCanada PipeLines Limited, a Canadian corporation (“Parent”), TransCanada PipeLine USA Ltd., a Nevada corporation and a wholly owned subsidiary of Parent (“US Parent”), Taurus Merger Sub Inc., a Delaware corporation and a wholly owned subsidiary of US Parent (“Merger Sub”), and, solely for purposes of Section 3.02, Section 5.02, Section 5.09 and Article VIII of the Merger Agreement, TransCanada Corporation, a Canadian corporation and the direct parent company of Parent (“TransCanada”). Upon the terms and subject to the conditions set forth in the Merger Agreement, Merger Sub will be merged with and into CPG (the “Merger”) with CPG surviving the Merger as an indirect wholly owned subsidiary of TransCanada. The Merger is expected to close in the second half of 2016, subject to satisfaction of customary conditions, including receipt of required regulatory and CPG shareholder approval. Following the completion of the transaction, TransCanada will own the general partner of the Partnership, all of the Partnership's incentive distribution rights and all of the Partnership's subordinated units, which represent a 46.5% limited partnership interest in the Partnership. The Condensed Consolidated and Combined Financial Statements (unaudited) have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (the "SEC"). Certain information and note disclosures normally included in annual financial statements prepared in accordance with GAAP have been condensed or omitted pursuant to those rules and regulations, although the Partnership believes that the disclosures made are adequate to make the information not misleading. These financial statements should be read in conjunction with the Predecessor’s combined financial statements included in the Partnership's Annual Report on Form 10-K for the year ended December 31, 2015 (the " 2015 Form 10-K"). These financial statements reflect all normal recurring adjustments that are, in the opinion of management, necessary to fairly present the Partnership’s results of operations and financial position in accordance with GAAP in the United States of America. Amounts reported in the Condensed Statements of Consolidated and Combined Operations (unaudited) are not necessarily indicative of amounts expected for the respective annual periods. All intercompany transactions and balances have been eliminated.

Initial Public Offering

Initial Public Offering	3 Months Ended
	Mar. 31, 2016
Equity [Abstract]
Initial Public Offering	Initial Public Offering On February 6, 2015, the Partnership's common units began trading on the New York Stock Exchange under the ticker symbol "CPPL." On February 11, 2015 , the Partnership completed its offering of 53,833,107 common units at a price to the public of $23.00 per unit, including 7,021,709 common units that were issued pursuant to the exercise in full of the underwriters' over-allotment option. The Partnership received net proceeds of $1,168.4 million from the offering. At or prior to the closing of the IPO the following transactions occurred: • CEG contributed $1,217.3 million of capital to certain subsidiaries of the Predecessor to repay intercompany debt owed to NiSource Finance. CEG entered into new intercompany debt agreements with NiSource Finance for $1,217.3 million ; • CEG contributed substantially all of the subsidiaries in the Predecessor to Columbia OpCo; • CEG assumed responsibility for all historical current and deferred income taxes other than Tennessee state income taxes that continue to be borne by the Partnership post-IPO, as well as associated regulatory assets and liabilities; • CEG contributed a 7.3% limited partner interest in Columbia OpCo to the Partnership in exchange for 46,811,398 subordinated units in the Partnership and all of the Partnership's incentive distribution rights; • The Partnership purchased from Columbia OpCo an additional 8.4% limited partner interest in exchange for $1,168.4 million from the net proceeds of the IPO, net of underwriting discounts, structuring fees and offering expenses of approximately $69.8 million , resulting in the Partnership owning a 15.7% limited partner interest in Columbia OpCo. The table below summarizes the effects of the changes in the Partnership's ownership interest in Columbia OpCo on the Partnership's equity: Three Months Ended (in millions) 2016 2015 Net income attributable to the Partnership $ 27.3 $ 13.3 Decrease in partnership equity for the purchase of an additional 8.4 percent interest in Columbia OpCo — (424.4 ) Change from net income attributable to the Partnership and transfers to noncontrolling interest $ 27.3 $ (411.1 ) • Columbia OpCo distributed $500.0 million to CEG as a reimbursement of preformation capital expenditures with respect to the assets contributed to Columbia OpCo. The Partnership entered into an omnibus agreement with CEG and its affiliates (together with a services agreement with CPGSC) at the closing of the IPO that addresses (1) centralized corporate, general and administrative services to be provided by CEG for the Partnership and the reimbursement by the Partnership for the Partnership's portion of these services, (2) the Partnership's right of first offer for CEG's 84.3% interest in Columbia OpCo, (3) the indemnification of the Partnership for certain potential environmental and toxic tort claims losses and expenses associated with the operation of the assets and occurring before the closing date of the IPO and (4) Columbia OpCo's requirement to guarantee future indebtedness that CPG incurs.

Recent Accounting Pronouncement

Recent Accounting Pronouncements	3 Months Ended
	Mar. 31, 2016
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the FASB issued ASU 2014-09, Revenue from Contracts with Customers (Topic 606). ASU 2014-09 outlines a single, comprehensive model for entities to use in accounting for revenue arising from contracts with customers and supersedes most current revenue recognition guidance. The core principle of the new standard is that an entity should recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In August 2015, the FASB issued ASU 2015-14 to extend the adoption date for ASU 2014-09 to periods beginning after December 15, 2017, including interim periods, and the new standard is to be applied retrospectively, with early adoption permitted on the original effective date of ASU 2014-09 on a limited basis. In March 2016, the FASB issued ASU 2016-08, which amends the principal-versus-agent implementation guidance and illustrations in ASU 2014-09. Among other things, ASU 2016-08 clarifies that an entity should evaluate whether it is the principal or the agent for each specified good or service promised in a contract with a customer. As defined in ASU 2016-08, a specified good or service is "a distinct good or service (or a distinct bundle of goods or services) to be provided to the customer." Therefore, for contracts involving more than one specified good or service, the entity may be the principal for one or more specified goods or services and the agent for others. ASU 2016-08 has the same effective date as ASU 2014-09, as amended by ASU 2015-14. The Partnership is required to adopt ASU 2016-08 using the same transition method it uses to adopt ASU 2014-09. The Partnership is currently evaluating the impact the adoption of ASU 2014-09, ASU 2015-14 and ASU 2016-08 will have on the Condensed Consolidated and Combined Financial Statements (unaudited) or Notes to Condensed Consolidated and Combined Financial Statements (unaudited). In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) . ASU 2016-02 introduces a lessee model that brings most leases on the balance sheet. The new standard also aligns many of the underlying principles of the new lessor model with those in ASC 606, the FASB's new revenue recognition standard (e.g., those related to evaluating when profit can be recognized). Furthermore, ASU 2016-02 addresses other concerns related to the current leases model. For example, ASU 2016-02 eliminates the requirement in current U.S. GAAP for an entity to use bright-line tests in determining lease classification. The standard also requires lessors to increase the transparency of their exposure to changes in value of their residual assets and how they manage that exposure. The Partnership is required to adopt ASU 2016-02 for periods beginning after December 15, 2018, including interim periods, with early adoption permitted. The Partnership is currently evaluating the impact the adoption of ASU 2016-02 will have on the Condensed Consolidated and Combined Financial Statements (unaudited) or Notes to Condensed Consolidated and Combined Financial Statements (unaudited). In April 2015, the FASB issued ASU 2015-03, Interest - Imputation of Interest (Subtopic 835-30): Simplifying the Presentation of Debt Issuance Costs. ASU 2015-03 changes the way entities present debt issuance costs in financial statements by presenting issuance costs on the balance sheet as a direct deduction from the related liability rather than as a deferred charge. Amortization of these costs will continue to be reported as interest expense. In August 2015, the FASB issued ASU 2015-15 to clarify the SEC staff's position on these costs in relation to line-of-credit agreements stating that the SEC staff would not object to an entity deferring and presenting debt issuance costs related to a line-of-credit arrangement as an asset and subsequently amortizing the deferred debt issuance costs ratably over the term of such arrangement, regardless of whether there are any outstanding borrowings on the line-of-credit. The Partnership retrospectively adopted ASU 2015-03 and ASU 2015-15 as of January 1, 2016. The adoption of this guidance did not have a material impact on the Condensed Consolidated or Combined Financial Statements (unaudited) or Notes to Condensed Consolidated and Combined Financial Statements (unaudited). In April 2015, the FASB issued ASU 2015-06, Earnings Per Share (Topic 260): Effects on Historical Earnings per Unit of Master Limited Partnership Dropdown Transactions. ASU 2015-06 specifies that for purposes of calculating historical earnings per unit under the two-class method, the earnings (losses) of a transferred business before the date of a dropdown transaction should be allocated entirely to the general partner. Qualitative disclosures about how the rights to the earnings (losses) differ before and after the dropdown transaction occurs for purposes of computing earnings per unit under the two-class method are also required. The Partnership retrospectively adopted ASU 2015-06 as of January 1, 2016. The adoption of this guidance did not have a material impact on the Condensed Consolidated and Combined Financial Statements (unaudited) or Notes to Condensed Consolidated and Combined Financial Statements (unaudited). In February 2015, the FASB issued ASU 2015-02, Consolidation (Topic 810): Amendments to the Consolidation Analysis . ASU 2015-02 amends consolidation guidance by including changes to the variable and voting interest models used by entities to evaluate whether an entity should be consolidated. The Partnership retrospectively adopted ASU 2015-02 as of January 1, 2016. The adoption of this guidance did not have a material impact on the Condensed Consolidated and Combined Financial Statements (unaudited) or Notes to Condensed Consolidated and Combined Financial Statements (unaudited).

Net Income Per Limited Partner

Net Income Per Limited Partner Unit	3 Months Ended
	Mar. 31, 2016
Net Income Per Limited Partner Unit [Abstract]
Net Income Per Limited Partner Unit	Net Income Per Limited Partner Unit Net income per unit applicable to common units and to subordinated units is computed by dividing the respective limited partners’ interest in net income by the weighted-average number of common units and subordinated units outstanding for the period. Because the Partnership has more than one class of participating securities, it uses the two-class method when calculating the net income per unit applicable to limited partners. The classes of participating securities include common units, subordinated units and incentive distribution rights. Basic and diluted net income per unit are the same because the Partnership does not have any potentially dilutive units outstanding for the periods presented. Pursuant to our cash distribution policy, within 60 days after the end of each quarter, we intend to distribute to the holders of common and subordinated units on a quarterly basis at least the minimum quarterly distribution of $0.1675 per unit, or $0.67 on an annualized basis, to the extent we have sufficient cash after establishment of cash reserves and payment of fees and expenses, including payments to our general partner and its affiliates. On May 2, 2016 , the board of directors of MLP GP, the Partnership's general partner, declared a quarterly cash distribution for the period January 1, 2016 , through March 31, 2016 , of $0.1875 per unit, or $18.9 million in total. This distribution is payable on May 20, 2016 , to unitholders of record as of May 13, 2016 . The calculation of net income per unit is as follows: Three Months Ended March 31, 2016 (in millions, except per unit data) Limited Partners' Common Units Limited Partners' Subordinated Units Incentive Distribution Rights Total Net income attributable to partners Distribution $ 10.1 $ 8.8 $ — $ 18.9 Net income in excess of distribution 3.3 2.8 2.3 8.4 Net income attributable to partners $ 13.4 $ 11.6 $ 2.3 $ 27.3 Weighted average limited partner units outstanding Basic and diluted 53.8 46.8 100.6 Net income attributable to partners' ownership interest per limited partner unit Basic and diluted $ 0.25 $ 0.25 $ 0.25 Three Months Ended March 31, 2015 (in millions, except per unit data) Limited Partners' Common Units Limited Partners' Subordinated Units Incentive Distribution Rights Total Net income attributable to partners Distribution $ — $ — $ — $ — Net income in excess of distribution (1) 7.1 6.2 — 13.3 Net income attributable to partners $ 7.1 $ 6.2 $ — $ 13.3 Weighted average limited partner units outstanding Basic and diluted 53.8 46.8 100.6 Net income attributable to partners' ownership interest subsequent to IPO per limited partner unit Basic and diluted $ 0.13 $ 0.13 $ 0.13 (1) Net income attributable to limited partners and in excess of distribution is for the period subsequent to the IPO.

Transactions With Affiliates

Transactions With Affiliates	3 Months Ended
	Mar. 31, 2016
Related Party Transactions [Abstract]
Transactions With Affiliates	Transactions with Affiliates Prior to CPG's separation from NiSource, the Partnership engaged in transactions with subsidiaries of NiSource which were deemed to be affiliates of the Partnership. The Partnership continues to engage in transactions with subsidiaries of CPG subsequent to the Separation. These affiliate transactions are summarized in the tables below: Statement of Operations Three Months Ended (in millions) 2016 2015 Transportation revenues $ — $ 28.7 Storage revenues — 13.3 Other revenues — 0.1 Operation and maintenance expense 42.4 36.1 Interest expense 7.2 11.4 Interest income 0.1 1.0 Balance Sheet (in millions) March 31, December 31, 2015 Accounts receivable $ 122.6 $ 149.4 Short-term borrowings 348.8 42.1 Accounts payable 22.6 86.3 Long-term debt 630.9 630.9 Transportation, Storage and Other Revenues . Prior to the Separation, the Partnership provided natural gas transportation, storage and other services to subsidiaries of NiSource, the Partnership's former affiliates. Prior to the IPO, the Predecessor provided similar services to subsidiaries of NiSource. Operation and Maintenance Expense . The Partnership receives executive, financial, legal, information technology and other administrative and general services from CPGSC. Prior to the IPO, the Predecessor received similar services from NiSource Corporate Services. Expenses incurred as a result of these services consist of employee compensation and benefits, outside services and other expenses. The expenses are charged directly or allocated using various allocation methodologies based on a combination of gross fixed assets, total operating expense, number of employees and other measures. Management believes the allocation methodologies are reasonable. However, these allocations and estimates may not represent the amounts that would have been incurred had the services been provided by an outside entity. Interest Expense and Income . The Partnership was charged interest for long-term debt of $7.7 million and $12.2 million for the three months ended March 31, 2016 and 2015 , respectively, offset by associated AFUDC of $0.7 million and $1.0 million for the three months ended March 31, 2016 and 2015 , respectively. Columbia OpCo and its subsidiaries entered into an intercompany money pool agreement with NiSource Finance, which became effective on the date of the IPO. Following the Separation, the agreement is now with CPG. The money pool is available for Columbia OpCo and its subsidiaries' general purposes, including capital expenditures and working capital. This intercompany money pool agreement is discussed in connection with Short-term Borrowings below. Prior to the IPO, the subsidiaries of the Predecessor participated in a similar money pool agreement with NiSource Finance. CPGSC administers the current money pool agreement. The cash accounts maintained by the subsidiaries of Columbia OpCo were, prior to the Separation, swept into a NiSource corporate account on a daily basis, creating an affiliated receivable or decreasing an affiliated payable, as appropriate, between NiSource and the subsidiary. Subsequent to the Separation, cash accounts maintained by the subsidiaries of Columbia OpCo are swept into a CPG corporate account on a daily basis, creating an affiliated receivable or decreasing an affiliated payable, as appropriate, between CPG and the subsidiary. The amount of interest expense and income for short-term borrowings is determined by the net position of each subsidiary in the money pool. The money pool weighted-average interest rate at March 31, 2016 and 2015 was 0.54% and 1.07% , respectively. For the three months ended March 31, 2016 and 2015 , the interest expense for short-term borrowings charged was $0.2 million . Accounts Receivable . The Partnership includes in accounts receivable amounts due from the money pool discussed above of $115.6 million and $140.5 million at March 31, 2016 and December 31, 2015 , respectively, for subsidiaries of Columbia OpCo in a net deposit position. Also, included in the balance at March 31, 2016 and December 31, 2015 are amounts due from subsidiaries of CPG, subsequent to the Separation, or NiSource, prior to the Separation, for transportation and storage services of $7.0 million and $8.9 million , respectively. Net cash flows related to the money pool receivables are included as Investing Activities on the Condensed Statements of Consolidated and Combined Cash Flows (unaudited). All other affiliated receivables are included as Operating Activities. Short-term Borrowings . In connection with the closing of the IPO, the subsidiaries of Columbia OpCo entered into an intercompany money pool agreement with NiSource Finance with $750.0 million of reserved borrowing capacity. Following the Separation, the agreement is now with CPG. In furtherance of the money pool agreement, CPG entered into a $1,500.0 million revolving credit agreement on December 5, 2014. The CPG revolving credit agreement became effective at the completion of the Separation with a termination date of July 2, 2020. Each of CEG, OpCo GP and Columbia OpCo is a guarantor of CPG's revolving credit facility. As a guarantor and restricted subsidiary, Columbia OpCo is subject to various customary covenants and restrictive provisions which, among other things, limit CPG’s and its restricted subsidiaries’ ability to incur additional indebtedness, guarantees and/or liens; consolidate, merge or transfer all or substantially all of their assets; make certain investments or restricted payments; modify certain material agreements; engage in certain types of transactions with affiliates; dispose of assets; and prepay certain indebtedness; each of which is subject to customary and usual exceptions and baskets, including an exception to the limitation on restricted payments for distributions of available cash, as permitted by their organizational documents. The restricted payment provision does not prohibit CPG of any of its restricted subsidiaries from making distributions in accordance with their respective organizational documents unless there has been an event of default (as defined in the revolving credit agreement), and neither CPG nor any of its restricted subsidiaries has any restrictions on its ability to make distributions under its organizational documents. Under Columbia OpCo's partnership agreement, it is required to distribute all of its available cash each quarter, less the amounts of cash reserves that OpCo GP determines are necessary or appropriate in its reasonable discretion to provide for the proper conduct of Columbia OpCo's business. In addition, subject to Delaware law, the board of directors of CPG may similarly determine whether to declare dividends at CPG without restriction under its revolving credit agreement. At March 31, 2016 , neither CPG nor its subsidiaries had any restricted assets. If Columbia OpCo and the other loan parties fail to perform their obligations under these and other covenants, it could adversely affect Columbia OpCo’s ability to finance future business opportunities and make cash distributions to the Partnership. CPG’s revolving credit facility also contains customary events of default, including cross default provisions that apply to any other indebtedness CPG may have with an outstanding principal amount in excess of $50.0 million . If a default occurred, the relevant lenders could elect to declare the debt, together with accrued interest and other fees, to be immediately due and payable and proceed against Columbia OpCo as a guarantor. The balance of Short-term Borrowings at March 31, 2016 and December 31, 2015 of $348.8 million and $42.1 million , respectively, includes those subsidiaries of Columbia OpCo and those subsidiaries of the Predecessor in a net borrower position of the money pool discussed above. Net cash flows related to Short-term Borrowings are included as Financing Activities on the Condensed Statements of Consolidated and Combined Cash Flows (unaudited). Accounts Payable . The affiliated accounts payable balance primarily includes amounts due for services received from CPGSC, subsequent to the Separation, NiSource Corporate Services, prior to the separation, and interest payable to CPG, subsequent to the Separation, and NiSource Finance, prior to the Separation. Long-term Debt . In May 2015, the Partnership's outstanding intercompany debt transferred from NiSource Finance to CPG. The Partnership’s long-term financing requirements are satisfied through borrowings from CPG. On January 31, 2016, the Partnership amended its intercompany credit agreement with CPG to extend the maturity date of the note originating on December 9, 2013 from December 31, 2016 to December 31, 2020. The Partnership may borrow at any time from the origination date to December 31, 2016 not to exceed $2.6 billion . From January 1, 2017 to December 31, 2020, the Partnership may borrow at any time not to exceed $2.3 billion . As of the January 2016 amendment, the note carries a fixed interest rate of 4.70% for the outstanding borrowings as of March 31, 2016 . Details of the long-term debt balance are summarized in the table below: Origination Date Interest Rate Maturity Date March 31, 2016 December 31, 2015 (in millions) December 9, 2013 4.70 % December 31, 2020 $ 630.9 $ 630.9 Dividends . During the three months ended March 31, 2016 , Columbia OpCo distributed $108.9 million to CEG. During the three months ended March 31, 2015 , Columbia OpCo distributed $500.0 million to CEG as a reimbursement of preformation capital expenditures with respect to the assets contributed to Columbia OpCo. There were no restrictions on the payment by the Partnership of distributions to CEG.

Short-Term Borrowings

Short-Term Borrowings	3 Months Ended
	Mar. 31, 2016
Short-term Debt [Abstract]
Short-Term Borrowings	Short-Term Borrowings On December 5, 2014, the Partnership entered into a $500.0 million senior revolving credit facility, of which $50.0 million in letters of credit is available. The revolving credit facility became effective at the closing of the IPO with a termination date of February 11, 2020. The credit facility is available for general partnership purposes, including working capital and capital expenditures, including the funding of capital calls. Obligations under the revolving credit facility are unsecured. The loans thereunder bear interest at the Partnership's option at either (i) the greatest of (a) the federal funds effective rate plus 0.500 percent , (b) the reference prime rate of Wells Fargo Bank, National Association or (c) the Eurodollar rate which is based on the LIBOR, plus 1.000 percent , each of which is subject to a margin that varies from 0.000 percent to 0.650 percent per annum, according to the credit rating of CPG, or (ii) the Eurodollar rate plus a margin that varies from 1.000 percent to 1.650 percent per annum, according to the credit rating of CPG. The revolving credit facility is subject to a facility fee that varies from 0.125 percent to 0.350 percent per annum, according to the credit rating of CPG. The revolving indebtedness under the credit facility ranks equally with all the Partnership's outstanding unsecured and unsubordinated debt. CPG, CEG, OpCo GP and Columbia OpCo each fully guarantee the credit facility. The revolving credit facility contains various covenants and restrictive provisions which, among other things, limit the Partnership's ability and its restricted subsidiaries’ ability to incur additional indebtedness, guarantees and/or liens; consolidate, merge or transfer all or substantially all of their assets; make certain investments or restricted payments; modify certain material agreements; engage in certain types of transactions with affiliates; dispose of assets; and prepay certain indebtedness; each of which is subject to customary and usual exceptions and baskets, including an exception to the limitation on restricted payments for distributions of available cash, as permitted by their organizational documents. The restricted payment provision does not prohibit the Partnership or any of its restricted subsidiaries from making distributions in accordance with their respective organizational documents unless there has been an event of default (as defined in the revolving credit agreement), and neither the Partnership nor any of its restricted subsidiaries has any restrictions on their ability to make distributions under their organization agreements. In particular, in accordance with the partnership agreement, the general partner has adopted a policy that the Partnership will make quarterly cash distributions in amounts equal to at least the minimum quarterly distribution of $0.1675 on each common and subordinated unit. However, the determination to make any distributions of cash is subject to the discretion of the general partner. At March 31, 2016 , neither the Partnership nor its consolidated subsidiaries had any restricted assets. If the Partnership fails to perform its obligations under these and other covenants, the revolving credit commitment could be terminated and any outstanding borrowings, together with accrued interest, under the revolving credit facility could be declared immediately due and payable. The revolving credit facility also contains customary events of default, including cross default provisions that apply to any other indebtedness the Partnership may have with an outstanding principal amount in excess of $50.0 million . The revolving credit facility also contains certain financial covenants that require the Partnership to maintain a consolidated total leverage ratio that does not exceed (i) 5.50 to 1.00 for the period of four consecutive fiscal quarters (each, a "test period") ending after December 31, 2015 and on or before December 31, 2017, and (ii) 5.00 to 1.00 for any test period ending after December 31, 2017, provided that after December 31, 2017 and during a Specified Acquisition Period (as defined in the revolving credit facility), the leverage ratio shall not exceed 5.50 to 1.00 . A breach of any of these covenants could result in a default in respect of the related debt. If a default occurred, the relevant lenders could elect to declare the debt, together with accrued interest and other fees, to be immediately due and payable and proceed against the Partnership or any guarantor. The Merger, if completed, would constitute a change of control under the terms of the Partnership's revolving credit facility. Accordingly, in connection with the closing of the Merger, the Partnership expects the revolving credit facility to be terminated and all outstanding amounts thereunder to be repaid and any existing letters of credit to be replaced. See Note 1, "Basis of Accounting Presentation" for additional information regarding the Merger. As of March 31, 2016 and December 31, 2015 , the Partnership had $15.0 million in outstanding borrowings and issued no letters of credit under the revolving credit facility. Short-term borrowings were as follows: (in millions) March 31, December 31, 2015 Credit facility borrowings, weighted average interest rate of 1.50% and 1.28% at March 31, 2016 and December 31, 2015, respectively $ 15.0 $ 15.0 Given their maturity and turnover is less than 90 days, cash flows related to the borrowings and repayments of the revolving credit facility are presented net in the Condensed Statements of Consolidated and Combined Cash Flows (unaudited).

Gain On Sale Of Assets

Gain On Sale Of Assets	3 Months Ended
	Mar. 31, 2016
Gain On Sale of Assets [Abstract]
Gain On Sale Of Assets	Gain on Sale of Assets The Partnership recognizes gains on conveyances of mineral rights positions into earnings as any obligation associated with conveyance is satisfied. For the three months ended March 31, 2016 and 2015 , gains on conveyances amounted to $2.6 million and $5.3 million , respectively, and are included in "Gain on sale of assets" on the Condensed Statements of Consolidated and Combined Operations (unaudited). As of March 31, 2016 and December 31, 2015 , deferred gains of approximately $5.5 million and $8.1 million , respectively, were deferred pending performance of future obligations and recorded within "Deferred revenue," on the Condensed Consolidated Balance Sheets (unaudited).

Goodwill

Goodwill	3 Months Ended
	Mar. 31, 2016
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill The Partnership tests its goodwill for impairment annually as of May 1 unless indicators, events, or circumstances would require an immediate review. Goodwill is tested for impairment using financial information at the reporting unit level, referred to as the Columbia Gas Transmission Operations reporting unit, which is consistent with the level of discrete financial information reviewed by management. The Columbia Gas Transmission Operations reporting unit includes the following entities: Columbia Gas Transmission (including its equity method investment in the Millennium Pipeline joint venture), Columbia Gulf and the equity method investment in Hardy Storage. All of the Partnership's goodwill relates to NiSource's acquisition of CEG in 2000, which was contributed to the Partnership prior to the IPO. The Partnership’s goodwill assets at March 31, 2016 were $1,975.5 million . The Predecessor completed a quantitative (“step 1”) fair value measurement of the reporting unit during the May 1, 2012 goodwill test. The test indicated that the fair value of the reporting unit substantially exceeded the carrying value, indicating that no impairment existed. GAAP allows entities testing goodwill for impairment the option of performing a qualitative (“step 0”) assessment before calculating the fair value of a reporting unit for the goodwill impairment test. If a step 0 assessment is performed, an entity is no longer required to calculate the fair value of a reporting unit unless the entity determines that, based on that assessment, it is more likely than not that its fair value is less than its carrying amount. The Partnership applied the qualitative step 0 analysis to its reporting unit for the annual impairment test performed as of May 1, 2015 . For the current year test, the Partnership assessed various assumptions, events and circumstances that would have affected the estimated fair value of the reporting unit as compared to its base line May 1, 2012 step 1 fair value measurement. The results of this assessment indicated that it is not more likely than not that its reporting unit fair value is less than the reporting unit carrying value. The Partnership considered whether there were any events or changes in circumstances subsequent to the annual test that would reduce the fair value of the reporting unit below its carrying amount and necessitate another goodwill impairment test. In consideration of all relevant factors, including the recent Merger Agreement, there were no indicators that would require goodwill impairment testing during the first quarter of 2016 .

Asset Retirement Obligations

Asset Retirement Obligations	3 Months Ended
	Mar. 31, 2016
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations Changes in the Partnership’s liability for asset retirement obligations for the three months ended March 31, 2016 and 2015 are presented in the table below: (in millions) 2016 2015 Balance as of January 1, $ 25.3 $ 23.2 Noncontributed net parent investment adjustments (1) — (0.4 ) Accretion expense 0.3 0.3 Additions — — Settlements — — Change in estimated cash flows (0.9 ) — Balance as of March 31, $ 24.7 $ 23.1 (1) Reflects the removal of amounts related to Crossroads Pipeline Company, which was included in the Predecessor but was not contributed to the Partnership. The asset retirement obligations above relate to the modernization program of pipelines and transmission facilities, the retiring of offshore facilities, polychlorinated biphenyl ("PCB") remediation and asbestos removal at several compressor and measuring stations. The Partnership recognizes that certain assets, which include gas pipelines and natural gas storage wells, will operate for an indeterminate future period when properly maintained. A liability for these asset retirement obligations will be recorded only if and when a future retirement obligation with a determinable life is identified.

Regulatory Matters

Regulatory Matters	3 Months Ended
	Mar. 31, 2016
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Columbia Gas Transmission Customer Settlement. In November 2015, Columbia Gas Transmission commenced the fourth year of the Columbia Gas Transmission long-term system modernization program. Columbia Gas Transmission expects to place approximately $300 million in modernization investments into service during the year. Recovery of approximately $320 million of investments made in 2015 began on February 1, 2016. In December 2015, Columbia Gas Transmission filed an extension of this settlement and received the FERC's approval of the customer agreement in March 2016.This extension will allow Columbia Gas Transmission to invest an additional $1.1 billion over an additional three-year period through 2020. This agreement also expands the scope of facility investments covered by the program. Columbia Gulf. On January 21, 2016, the FERC issued an Order (the "January 21 Order") initiating an investigation pursuant to Section 5 of the NGA to determine whether Columbia Gulf ’s existing rates for jurisdictional services are unjust and unreasonable. Columbia Gulf filed a cost and revenue study with the FERC on April 5, 2016, as required by the January 21 Order. The January 21 Order directed that a hearing be conducted pursuant to an accelerated timeline and that an initial decision be issued by February 28, 2017. The outcome of this proceeding to Columbia Gulf is not currently determinable. Cost Recovery Trackers and other similar mechanisms. A significant portion of the transmission and storage regulated companies' revenue is related to the recovery of their operating costs, the review and recovery of which occurs via standard regulatory proceedings with the FERC under Section 4 of the NGA. However, certain operating costs of the Columbia OpCo regulated transmission and storage companies are significant and recurring in nature, such as fuel for compression and lost and unaccounted for gas. The FERC allows for the recovery of such costs via cost tracking mechanisms. These tracking mechanisms allow the transmission and storage companies' rates to fluctuate in response to changes in certain operating costs or conditions as they occur to facilitate the timely recovery of its costs incurred. The tracking mechanisms involve a rate adjustment that is filed at a predetermined frequency, typically annually, with the FERC and is subject to regulatory review before new rates go into effect. Other such costs under regulatory tracking mechanisms include upstream pipeline transmission, electric compression, operational purchases and sales of natural gas, and the revenue requirement for capital investments made under Columbia Gas Transmission's long-term plan to modernize its interstate transmission system as discussed above.

Equity Method Investments

Equity Method Investments	3 Months Ended
	Mar. 31, 2016
Equity Method Investments [Abstract]
Equity Method Investments	Equity Method Investments Certain investments of the Partnership are accounted for under the equity method of accounting. These investments are recorded within "Unconsolidated Affiliates" on the Partnership's Condensed Consolidated Balance Sheets (unaudited) and the Partnership's portion of the results is reflected in "Equity Earnings in Unconsolidated Affiliates" on the Partnership's Condensed Statements of Consolidated and Combined Operations (unaudited). These investments are integral to the Partnership’s business. Contributions are made to these equity investees to fund the Partnership’s share of capital projects. The following table contains contribution and distribution data representing the Partnership's portion based on the Partnership's ownership percentage of each investment: Three Months Ended (in millions) 2016 2015 Millennium Pipeline Contributions to Millennium Pipeline $ 1.9 $ — Distributions of earnings from Millennium Pipeline 15.2 16.6 Hardy Storage Contributions to Hardy Storage — — Distributions of earnings from Hardy Storage 0.7 0.5 Pennant Contributions to Pennant — — Distributions of earnings from Pennant 3.0 1.2 Return of capital from Pennant 0.2 1.3

Income Taxes

Income Taxes	3 Months Ended
	Mar. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The Partnership is a limited partnership and is treated as a partnership for U.S. federal income tax purposes and, therefore, is not liable for entity-level federal income taxes. Amounts presented for 2015 in the combined financial statements relate to income taxes that have been determined on a separate tax return basis for the period prior to the IPO. The effective tax rates for the three months ended March 31, 2016 and 2015 were zero and 15.3% , respectively. The effective tax rate for 2015 differs from the Federal tax rate of 35% primarily due to post-IPO income that is not subject to income tax at the partnership level.

Pension And Other Postretiremen

Pension And Other Postretirement Benefits	3 Months Ended
	Mar. 31, 2016
Pension and Other Postretirement Benefit Expense [Abstract]
Pension And Other Postretirement Benefits	Pension and Other Postretirement Benefits CPG provides defined contribution plans and noncontributory defined benefit retirement plans that cover employees of subsidiaries of Columbia OpCo. Prior to the Separation, employees of subsidiaries of Columbia OpCo were covered by defined contribution plans and noncontributory defined benefit retirement plans provided by NiSource. Benefits under the defined benefit retirement plans reflect the employees’ compensation, years of service and age at retirement. Additionally, CPG provides health care and life insurance benefits for certain retired employees of subsidiaries of Columbia OpCo. The majority of employees may become eligible for these benefits if they reach retirement age while working for subsidiaries of Columbia OpCo. The expected cost of such benefits is accrued during the employees’ years of service. Current rates charged to customers of subsidiaries of Columbia OpCo include postretirement benefit costs. Cash contributions are remitted to grantor trusts. Subsidiaries of Columbia OpCo are participants in the consolidated CPG defined benefit retirement plans (the "Plans") and, therefore, subsidiaries of Columbia OpCo are allocated a ratable portion of CPG’s grantor trusts for the Plans in which its employees and retirees participate. As a result, the Partnership follows multiple employer accounting under the provisions of GAAP. The following table provides the components of the subsidiaries of Columbia OpCo's allocation of net periodic benefits cost for the three months ended March 31, 2016 and 2015 : Pension Benefits Other Postretirement Three Months Ended March 31, (in millions) 2016 2015 2016 2015 Components of Net Periodic Benefit Cost (Income) Service cost $ 1.3 $ 1.3 $ 0.2 $ 0.3 Interest cost 3.2 3.1 1.0 1.0 Expected return on assets (5.5 ) (6.1 ) (3.8 ) (4.3 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Recognized actuarial loss 2.5 2.0 — — Total Net Periodic Benefit Cost (Income) $ 1.3 $ 0.1 $ (2.6 ) $ (3.0 )

Fair Value

Fair Value	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value	Fair Value The Partnership has certain financial instruments that are not measured at fair value on a recurring basis but nevertheless are recorded at amounts that approximate fair value due to their liquid or short-term nature, including cash and cash equivalents, customer deposits, short-term borrowings and short-term borrowings-affiliated. The Partnership's long-term debt-affiliated is recorded at historical amounts. The following methods and assumptions were used to estimate the fair value of each class of financial instruments for which it is practicable to estimate fair value. Long-term debt-affiliated. The fair values of these securities are estimated based on the quoted market prices for similar issues or on the rates offered for securities of the same remaining maturities. On January 31, 2016, the Partnership amended its intercompany credit agreement to extend the maturity date and apply a fixed interest rate. Prior to this amendment, the fair value approximated the carrying value as these securities bore interest at variable rates. These fair value measurements are classified as Level 2 within the fair value hierarchy. For the three months ended March 31, 2016 and for the year ended December 31, 2015 , there were no changes in the method or significant assumptions used to estimate the fair value of the financial instruments. The carrying amount and estimated fair values of financial instruments were as follows: (in millions) Carrying Amount as of March 31, 2016 Estimated Fair Value as of March 31, 2016 Carrying Amount as of Dec. 31, 2015 Estimated Fair Value as of Dec. 31, 2015 Long-term debt-affiliated $ 630.9 $ 652.8 $ 630.9 $ 630.9

Other Commitments And Contingen

Other Commitments And Contingencies	3 Months Ended
	Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Other Commitments and Contingencies A. Guarantees and Indemnities. In the normal course of its business, the Partnership and certain subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of the parent or certain subsidiaries. Such agreements include guarantees and stand-by letters of credit. These agreements are entered into primarily to support or enhance the creditworthiness otherwise attributed to the parent or a subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the parent or the subsidiaries' intended commercial purposes. The total guarantees and indemnities in existence at March 31, 2016 and the years in which they expire were: (in millions) Total 2016 2017 2018 2019 2020 After Guarantees of debt $ 2,750.0 $ — $ — $ 500.0 $ — $ 750.0 $ 1,500.0 Letters of credit 18.1 18.1 — — — — — Total commercial commitments $ 2,768.1 $ 18.1 $ — $ 500.0 $ — $ 750.0 $ 1,500.0 Guarantees of Debt. OpCo GP and Columbia OpCo (together with CEG, the "Guarantors") have guaranteed payment of $2,750.0 million in aggregated principal amount of CPG's senior notes. Each Guarantor is required to comply with covenants under the debt indenture and in the event of default the Guarantors would be obligated to pay the debt's principal and related interest. The Partnership does not anticipate that OpCo GP or Columbia OpCo will have any difficulty maintaining compliance. The guarantees of any Guarantor may be released under certain circumstances. First, if CPG discharges or defeases its obligations with respect to any series of CPG’s senior notes, then any guarantee will be released with respect to that series. Second, if no event of default has occurred and is continuing under the indenture, a Guarantor will be automatically and unconditionally released and discharged from its guarantee (i) at any time after June 1, 2018, upon any sale, exchange or transfer, whether by way of merger or otherwise, to any person that is not CPG’s affiliate, of all of CPG’s direct or indirect limited partnership, limited liability or other equity interests in the Guarantor; (ii) upon the merger of a guarantor into CPG or any other Guarantor or the liquidation and dissolution of such Guarantor; or (iii) at any time after June 1, 2018, upon release of all guarantees or other obligations of the Guarantor with respect to any of CPG’s funded debt, except CPG’s senior notes. Lines and Letters of Credit. The Partnership maintains a $500.0 million senior revolving credit facility, of which $50.0 million is available for issuance of letters of credit. The purpose of the facility is to provide cash for general partnership purposes, including working capital, capital expenditures, and the funding of capital calls. As of March 31, 2016 , the Partnership had $15.0 million in outstanding borrowings and no letters of credit under the revolving credit facility. CPG maintains a $1,500.0 million senior revolving credit facility, of which $250.0 million in letters of credit is available. CPG expects that $750.0 million of the facility will be utilized as credit support for Columbia OpCo and its subsidiaries and the remaining $750.0 million of the facility will be available for CPG’s general corporate purposes, including working capital. The revolving credit facility will provide liquidity support for CPG's $1,000.0 million commercial paper program. OpCo GP and Columbia OpCo, together with CEG, have each fully guaranteed the CPG credit facility. As of March 31, 2016 , CPG had no borrowings outstanding and $18.1 million in letters of credit outstanding under its revolving credit facility. CPG has established a commercial paper program (the “Program”) pursuant to which CPG may issue short-term promissory notes (the “Promissory Notes”) pursuant to the exemption from registration contained in Section 4(a)(2) of the Securities Act of 1933, as amended (the "Securities Act"). Amounts available under the Program may be borrowed, repaid and re-borrowed from time to time, with the aggregate face or principal amount of the Promissory Notes outstanding under the Program at any time not to exceed $1,000.0 million . OpCo GP and Columbia OpCo, together with CEG, have each agreed, jointly and severally, unconditionally and irrevocably to guarantee payment in full of the principal of and interest (if any) on the Promissory Notes. The net proceeds of issuances of the Promissory Notes are expected to be used for general corporate purposes. As of March 31, 2016 , CPG had no Promissory Notes outstanding under the Program. B. Other Legal Proceedings. In the normal course of its business, the Partnership has been named as a defendant in various legal proceedings. In the opinion of management, the ultimate disposition of these currently asserted claims will not have a material impact on the Partnership’s consolidated and combined financial statements. C. Environmental Matters. The Partnership's operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. The Partnership believes that it is in substantial compliance with those environmental regulations currently applicable to its operations and believes that it has all necessary material permits to conduct its operations. It is the Partnership's continued intent to address environmental issues in cooperation with regulatory authorities in such a manner as to achieve mutually acceptable compliance plans. However, there can be no assurance that fines and penalties will not be incurred. The Partnership records accruals to cover environmental remediation at various sites. The current portion of this accrual is included in “Other accruals” in the Condensed Consolidated Balance Sheets (unaudited). The noncurrent portion is included in “Other noncurrent liabilities” in the Condensed Consolidated Balance Sheets (unaudited). Air The CAA and comparable state laws regulate emissions of air pollutants from various industrial sources, including compressor stations, and also impose various monitoring and reporting requirements. Such laws and regulations may require pre-approval for the construction or modification of certain projects or facilities expected to produce air emissions or result in an increase of existing air emissions; application for, and strict compliance with, air permits containing various emissions and operational limitations; or the utilization of specific emission control technologies to limit emissions. The actions listed below could require further reductions in emissions from various emission sources. The Partnership will continue to closely monitor developments in these matters. National Ambient Air Quality Standards. The federal CAA requires the EPA to set NAAQS for particulate matter and five other pollutants considered harmful to public health and the environment. Periodically, the EPA imposes new or modifies existing NAAQS. States that contain areas that do not meet the new or revised standards must take steps to maintain or achieve compliance with the standards. These steps could include additional pollution controls on boilers, engines, turbines, and other facilities owned by gas transmission operations. The following NAAQS were recently added or modified: Ozone : On October 1, 2015, the EPA issued a final rule lowering the NAAQS for ground-level ozone to 70 ppb under both the primary and secondary standards to provide requisite protection of public health and welfare, respectively. The EPA is required to include an adequate margin of safety in establishing the primary ozone standard for protection of public health, whereas the secondary ozone standard is intended to improve protection for trees, plants and ecosystems. The final rule becomes effective sixty days after the rule is published in the Federal Register. The EPA is required to make attainment and non-attainment designations for specific geographic locations under the revised standards by October 1, 2017 and, depending on the severity of the ozone present, non-attainment areas will have until between 2020 and 2037 to meet the health standard. With the EPA lowering the ground-level ozone standard, states may be required to implement more stringent regulations. Based on the current version of the rule, the Partnership does not expect a material impact on its operations. Nitrogen Dioxide (NO2) : The EPA revised the NO2 NAAQS by adding a one-hour standard while retaining the annual standard. The new standard could impact some CPG combustion sources. The EPA designated all areas of the country as unclassifiable/attainment in January 2012. After the establishment of a new monitoring network and possible modeling implementation, areas will potentially be re-designated sometime in 2016. States with areas that do not meet the standard will be required to develop rules to bring areas into compliance within five years of designation. Additionally, under certain permitting circumstances, emissions from some existing Partnership combustion sources may need to be assessed and mitigated. The Partnership will continue to monitor this matter and cannot estimate the impact of these rules at this time. Climate Change. Future legislative and regulatory programs could significantly restrict emissions of greenhouse gases including methane. New Source Performance Standards : On August 18, 2015, the EPA proposed to regulate fugitive methane emissions for compressor stations in the natural gas transmission and storage sector. The proposed rule was subsequently published in the Federal Register on September 18, 2015. Semiannual leak detection and repair requirements using optical gas imaging are proposed for all components at new or existing compressor stations. Existing compressor stations trigger leak detection and repair requirements if any unit at the facility is modified. The EPA proposed additional requirements for any new or modified centrifugal or reciprocating compressors. Replacement of wet seals with dry seals or demonstrating a 95% reduction of methane emissions from wet seals is proposed for centrifugal compressors and rod packing replacement for reciprocating compressors is proposed every 26,000 hours of operation or every three years. The Partnership will continue to monitor this matter and cannot estimate the impact of these rules at this time. Pipeline Safety On March 17, 2016, the federal Pipeline and Hazardous Materials Safety Administration (“PHMSA”) announced a proposed rulemaking that would, if adopted, impose more stringent requirements for certain gas lines and gathering lines under varying circumstances. Among other things, the proposed rulemaking would extend certain of PHMSA’s current regulatory safety programs for gas pipelines beyond “high consequence areas” to cover gas pipelines found in newly defined “moderate consequence areas” that contain as few as 5 dwellings within the potential impact area; require gas pipelines installed before 1970 that are currently exempted from certain pressure testing obligations to be tested to determine their maximum allowable operating pressures (“MAOP”); and require gathering lines in Class I areas, both onshore and offshore, to comply with standards regarding damage prevention, corrosion control (for metallic pipe), public education, MAOP limits, line markers and emergency planning if such gathering lines’ nominal design is 8 inches or more. In order to provide clarity and greater certainty on what may constitute a “gathering line,” PHMSA is proposing a new definition of that term under the rulemaking, which term would now encompass “a pipeline, or a connected series of pipelines, and equipment used to collect gas from the endpoint of a production facility/operation and transport it to the furthermost point downstream of the following endpoints” including the “inlet of 1 st gas processing plant;” the “outlet of” a gas treatment facility (not associated with a processing plant or compressor station); the “[o]utlet of the furthermost downstream compressor” leading to a pipeline, or the “point where separate production fields are commingled.” Other new requirements proposed by PHMSA under the rulemaking would require pipeline operators to: report to PHMSA in the event of certain MAOP exceedances; strengthen PHMSA integrity management requirements; consider seismicity in evaluating threats to a pipeline; conduct hydrostatic testing for all pipeline segments manufactured using longitudinal seam welds; and use more detailed guidance from PHMSA in the selection of assessment methods to inspect pipelines. Adoption of some or all of these standards under the proposed rulemaking could cause us to incur increased capital costs and costs of operation, which could be significant.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	3 Months Ended
	Mar. 31, 2016
Other Comprehensive Income (Loss), Tax [Abstract]
Accumulated Other Comprehensive Loss	Accumulated Other Comprehensive Loss The following tables display the components of Accumulated Other Comprehensive Loss for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2016 $ (3.9 ) $ (0.1 ) $ (4.0 ) Other comprehensive income before reclassifications — — — Amounts reclassified from accumulated other comprehensive income (2) 0.5 — 0.5 Net current-period other comprehensive income 0.5 — 0.5 Allocation of accumulated other comprehensive loss to noncontrolling interest 0.4 — 0.4 Balance as of March 31, 2016 $ (3.8 ) $ (0.1 ) $ (3.9 ) (1) Amounts in parentheses indicate debits. (2) Includes amounts allocated to noncontrolling interest. Three Months Ended March 31, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2015 $ (16.6 ) $ (0.1 ) $ (16.7 ) Predecessor net tax liabilities not assumed by Columbia OpCo (2) (10.2 ) (0.1 ) (10.3 ) Other comprehensive income before reclassifications — — — Amounts reclassified from accumulated other comprehensive income (3) 0.1 — 0.1 Net current-period other comprehensive income 0.1 — 0.1 Allocation of accumulated other comprehensive loss to noncontrolling interest (22.6 ) (0.1 ) (22.7 ) Balance as of March 31, 2015 $ (4.1 ) $ (0.1 ) $ (4.2 ) (1) All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits. (2) Reflects the non-cash elimination of all historical current and deferred income taxes other than Tennessee state income taxes that will continue to be borne by the Partnership post-IPO. (3) Includes amounts allocated to noncontrolling interest. Equity Investment Millennium Pipeline is an equity method investment and, therefore, Columbia OpCo is required to recognize a proportional share of Millennium Pipeline’s OCI. The remaining unrecognized loss at March 31, 2016 of $24.8 million , before tax, related to terminated interest rate swaps is being amortized over a 15 year period ending June 2025 into earnings using the effective interest method through interest expense as interest payments are made by Millennium Pipeline. The unrecognized loss of $24.8 million and $25.0 million , before tax, at March 31, 2016 and December 31, 2015 , respectively, is included in gains and losses on cash flow hedges above.

Other, Net

Other, Net	3 Months Ended
	Mar. 31, 2016
Other Nonoperating Income (Expense) [Abstract]
Other, Net	Other, Net Three Months Ended (in millions) 2016 2015 AFUDC Equity $ 6.1 $ 3.5 Miscellaneous — 0.8 Total Other, net $ 6.1 $ 4.3

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	3 Months Ended
	Mar. 31, 2016
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information The following table provides additional information regarding the Partnership’s Condensed Statements of Consolidated and Combined Cash Flows (unaudited) for the three months ended March 31, 2016 and 2015 : (in millions) 2016 2015 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities (1) $ 119.2 $ 98.8 Schedule of interest paid: Cash paid for interest, net of interest capitalized amounts $ 7.5 $ 15.6 (1) Capital expenditures included in current liabilities is comprised of "Accrued capital expenditures" and certain other amounts included within "Accounts payable" on the Condensed Consolidated Balance Sheets (unaudited).

Concentration Of Credit Risk

Concentration Of Credit Risk	3 Months Ended
	Mar. 31, 2016
Risks and Uncertainties [Abstract]
Concentration Risk Disclosure	Concentration of Credit Risk Columbia Gas of Ohio, an affiliated party prior to the Separation, accounted for greater than 10% of total operating revenues for the three months ended March 31, 2016 and 2015 . The following tables provide this customer's operating revenues and percentage of total operating revenues for the three months ended March 31, 2016 and 2015 : Three Months Ended March 31, 2016 2015 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 50.4 13.9 % $ 48.9 14.4 % (1) Represents the gross amount of revenue contracted for with Columbia Gas of Ohio and, therefore, subject to risk at the loss of this customer. Columbia Gas of Ohio has entered into certain capacity release arrangements with third parties which ultimately can decrease the net revenue amount the Partnership receives from Columbia Gas of Ohio in any given period. The loss of a significant portion of operating revenues from this customer could have a material adverse effect on the business of the Partnership.

Subsequent Event

Subsequent Event	3 Months Ended
	Mar. 31, 2016
Subsequent Events [Abstract]
Subsequent Event	Subsequent Event Distribution. On May 2, 2016 , the board of directors of MLP GP, the Partnership's general partner, declared a quarterly cash distribution for the period January 1, 2016 , through March 31, 2016 , of $0.1875 per unit, or $18.9 million in total. This distribution is payable on May 20, 2016 , to unitholders of record as of May 13, 2016 .

Initial Public Offering (Tables

Initial Public Offering (Tables)	3 Months Ended
	Mar. 31, 2016
Equity [Abstract]
Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest	Three Months Ended (in millions) 2016 2015 Net income attributable to the Partnership $ 27.3 $ 13.3 Decrease in partnership equity for the purchase of an additional 8.4 percent interest in Columbia OpCo — (424.4 ) Change from net income attributable to the Partnership and transfers to noncontrolling interest $ 27.3 $ (411.1 )

Net Income Per Limited Partne31

Net Income Per Limited Partner Unit (Tables)	3 Months Ended
	Mar. 31, 2016
Net Income Per Limited Partner Unit [Abstract]
Schedule Of Net Income Per Limited Partner Unit	Three Months Ended March 31, 2016 (in millions, except per unit data) Limited Partners' Common Units Limited Partners' Subordinated Units Incentive Distribution Rights Total Net income attributable to partners Distribution $ 10.1 $ 8.8 $ — $ 18.9 Net income in excess of distribution 3.3 2.8 2.3 8.4 Net income attributable to partners $ 13.4 $ 11.6 $ 2.3 $ 27.3 Weighted average limited partner units outstanding Basic and diluted 53.8 46.8 100.6 Net income attributable to partners' ownership interest per limited partner unit Basic and diluted $ 0.25 $ 0.25 $ 0.25 Three Months Ended March 31, 2015 (in millions, except per unit data) Limited Partners' Common Units Limited Partners' Subordinated Units Incentive Distribution Rights Total Net income attributable to partners Distribution $ — $ — $ — $ — Net income in excess of distribution (1) 7.1 6.2 — 13.3 Net income attributable to partners $ 7.1 $ 6.2 $ — $ 13.3 Weighted average limited partner units outstanding Basic and diluted 53.8 46.8 100.6 Net income attributable to partners' ownership interest subsequent to IPO per limited partner unit Basic and diluted $ 0.13 $ 0.13 $ 0.13 (1) Net income attributable to limited partners and in excess of distribution is for the period subsequent to the IPO.

Transactions With Affiliates (T

Transactions With Affiliates (Tables)	3 Months Ended
	Mar. 31, 2016
Related Party Transactions [Abstract]
Schedule of Transactions With Affiliates	Statement of Operations Three Months Ended (in millions) 2016 2015 Transportation revenues $ — $ 28.7 Storage revenues — 13.3 Other revenues — 0.1 Operation and maintenance expense 42.4 36.1 Interest expense 7.2 11.4 Interest income 0.1 1.0 Balance Sheet (in millions) March 31, December 31, 2015 Accounts receivable $ 122.6 $ 149.4 Short-term borrowings 348.8 42.1 Accounts payable 22.6 86.3 Long-term debt 630.9 630.9
Schedule of Related Party Transactions, Long-Term Debt	Origination Date Interest Rate Maturity Date March 31, 2016 December 31, 2015 (in millions) December 9, 2013 4.70 % December 31, 2020 $ 630.9 $ 630.9

Short-Term Borrowings (Tables)

Short-Term Borrowings (Tables)	3 Months Ended
	Mar. 31, 2016
Short-term Debt [Abstract]
Schedule of Short-Term Borrowings	(in millions) March 31, December 31, 2015 Credit facility borrowings, weighted average interest rate of 1.50% and 1.28% at March 31, 2016 and December 31, 2015, respectively $ 15.0 $ 15.0

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	3 Months Ended
	Mar. 31, 2016
Asset Retirement Obligation [Abstract]
Changes In Company's Liability For Asset Retirement Obligations	(in millions) 2016 2015 Balance as of January 1, $ 25.3 $ 23.2 Noncontributed net parent investment adjustments (1) — (0.4 ) Accretion expense 0.3 0.3 Additions — — Settlements — — Change in estimated cash flows (0.9 ) — Balance as of March 31, $ 24.7 $ 23.1 (1) Reflects the removal of amounts related to Crossroads Pipeline Company, which was included in the Predecessor but was not contributed to the Partnership.

Equity Method Investments (Tabl

Equity Method Investments (Tables)	3 Months Ended
	Mar. 31, 2016
Equity Method Investments [Abstract]
Equity Method Investments	The following table contains contribution and distribution data representing the Partnership's portion based on the Partnership's ownership percentage of each investment: Three Months Ended (in millions) 2016 2015 Millennium Pipeline Contributions to Millennium Pipeline $ 1.9 $ — Distributions of earnings from Millennium Pipeline 15.2 16.6 Hardy Storage Contributions to Hardy Storage — — Distributions of earnings from Hardy Storage 0.7 0.5 Pennant Contributions to Pennant — — Distributions of earnings from Pennant 3.0 1.2 Return of capital from Pennant 0.2 1.3

Pension And Other Postretirem36

Pension And Other Postretirement Benefits (Tables)	3 Months Ended
	Mar. 31, 2016
Pension and Other Postretirement Benefit Expense [Abstract]
Components Of The Plans' Net Periodic Benefits Cost	Pension Benefits Other Postretirement Three Months Ended March 31, (in millions) 2016 2015 2016 2015 Components of Net Periodic Benefit Cost (Income) Service cost $ 1.3 $ 1.3 $ 0.2 $ 0.3 Interest cost 3.2 3.1 1.0 1.0 Expected return on assets (5.5 ) (6.1 ) (3.8 ) (4.3 ) Amortization of prior service credit (0.2 ) (0.2 ) — — Recognized actuarial loss 2.5 2.0 — — Total Net Periodic Benefit Cost (Income) $ 1.3 $ 0.1 $ (2.6 ) $ (3.0 )

Fair Value (Tables)

Fair Value (Tables)	3 Months Ended
	Mar. 31, 2016
Fair Value Disclosures [Abstract]
Carrying Amount And Estimated Fair Values Of Financial Instruments	(in millions) Carrying Amount as of March 31, 2016 Estimated Fair Value as of March 31, 2016 Carrying Amount as of Dec. 31, 2015 Estimated Fair Value as of Dec. 31, 2015 Long-term debt-affiliated $ 630.9 $ 652.8 $ 630.9 $ 630.9

Other Commitments And Conting38

Other Commitments And Contingencies (Tables)	3 Months Ended
	Mar. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Guarantee Obligations	The total guarantees and indemnities in existence at March 31, 2016 and the years in which they expire were: (in millions) Total 2016 2017 2018 2019 2020 After Guarantees of debt $ 2,750.0 $ — $ — $ 500.0 $ — $ 750.0 $ 1,500.0 Letters of credit 18.1 18.1 — — — — — Total commercial commitments $ 2,768.1 $ 18.1 $ — $ 500.0 $ — $ 750.0 $ 1,500.0

Accumulated Other Comprehensi39

Accumulated Other Comprehensive Loss (Tables)	3 Months Ended
	Mar. 31, 2016
Other Comprehensive Income (Loss), Tax [Abstract]
Components Of Accumulated Other Comprehensive Loss	Three Months Ended March 31, 2016 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2016 $ (3.9 ) $ (0.1 ) $ (4.0 ) Other comprehensive income before reclassifications — — — Amounts reclassified from accumulated other comprehensive income (2) 0.5 — 0.5 Net current-period other comprehensive income 0.5 — 0.5 Allocation of accumulated other comprehensive loss to noncontrolling interest 0.4 — 0.4 Balance as of March 31, 2016 $ (3.8 ) $ (0.1 ) $ (3.9 ) (1) Amounts in parentheses indicate debits. (2) Includes amounts allocated to noncontrolling interest. Three Months Ended March 31, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of January 1, 2015 $ (16.6 ) $ (0.1 ) $ (16.7 ) Predecessor net tax liabilities not assumed by Columbia OpCo (2) (10.2 ) (0.1 ) (10.3 ) Other comprehensive income before reclassifications — — — Amounts reclassified from accumulated other comprehensive income (3) 0.1 — 0.1 Net current-period other comprehensive income 0.1 — 0.1 Allocation of accumulated other comprehensive loss to noncontrolling interest (22.6 ) (0.1 ) (22.7 ) Balance as of March 31, 2015 $ (4.1 ) $ (0.1 ) $ (4.2 ) (1) All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits. (2) Reflects the non-cash elimination of all historical current and deferred income taxes other than Tennessee state income taxes that will continue to be borne by the Partnership post-IPO. (3) Includes amounts allocated to noncontrolling interest.

Other, Net (Tables)

Other, Net (Tables)	3 Months Ended
	Mar. 31, 2016
Other Nonoperating Income (Expense) [Abstract]
Schedule Of Other, Net	Three Months Ended (in millions) 2016 2015 AFUDC Equity $ 6.1 $ 3.5 Miscellaneous — 0.8 Total Other, net $ 6.1 $ 4.3

Supplemental Cash Flow Inform41

Supplemental Cash Flow Information (Tables)	3 Months Ended
	Mar. 31, 2016
Supplemental Cash Flow Information [Abstract]
Additional Information Regarding Condensed Statements Of Consolidated Cash Flows	(in millions) 2016 2015 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities (1) $ 119.2 $ 98.8 Schedule of interest paid: Cash paid for interest, net of interest capitalized amounts $ 7.5 $ 15.6 (1) Capital expenditures included in current liabilities is comprised of "Accrued capital expenditures" and certain other amounts included within "Accounts payable" on the Condensed Consolidated Balance Sheets (unaudited).

Concentration Of Credit Risk (T

Concentration Of Credit Risk (Tables)	3 Months Ended
	Mar. 31, 2016
Risks and Uncertainties [Abstract]
Schedule of Concentration Of Credit Risk	Three Months Ended March 31, 2016 2015 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 50.4 13.9 % $ 48.9 14.4 % (1) Represents the gross amount of revenue contracted for with Columbia Gas of Ohio and, therefore, subject to risk at the loss of this customer. Columbia Gas of Ohio has entered into certain capacity release arrangements with third parties which ultimately can decrease the net revenue amount the Partnership receives from Columbia Gas of Ohio in any given period.

Basis of Accounting Presentat43

Basis of Accounting Presentation (Narrative) (Details)	3 Months Ended
	Mar. 31, 2016mi
Basis Of Accounting Presentation [Line Items]
Pipeline Miles	15,000
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	15.70%
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Additional Ownership Interest	46.50%
Corporate Joint Venture [Member]
Basis Of Accounting Presentation [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest	84.30%

Initial Public Offering (Narrat

Initial Public Offering (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	2 Months Ended	3 Months Ended
	Feb. 11, 2015	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Initial Public Offering [Line Items]
Contribution of capital from parent	$ 1,217.3
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Additional Ownership Interest			46.50%
Net proceeds from IPO		$ 1,168.4
Underwriting discounts, structuring fees, and offering expenses		$ 69.8
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest			15.70%
Common Units
Initial Public Offering [Line Items]
Shares Issued, Price Per Share	$ 23
Partners' Capital Account, Units, Sold in Public Offering		53,833,107
Over-Allotment Option [Member] | Common Units
Initial Public Offering [Line Items]
Partners' Capital Account, Units, Sold in Public Offering		7,021,709
Columbia Energy Group
Initial Public Offering [Line Items]
Contribution of capital from parent	$ 1,217.3
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		7.30%
Columbia Energy Group | Subordinated Units
Initial Public Offering [Line Items]
Partners' Capital Account, Units, Sold in Public Offering		46,811,398
Columbia OpCo
Initial Public Offering [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Additional Ownership Interest		8.40%
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		15.70%
Reimbursement of Preformation Capital				$ 500
Limited Partner | Common Units
Initial Public Offering [Line Items]
Contribution of capital from parent	0
Net proceeds from IPO		$ 1,168.4
Limited Partner | Subordinated Units
Initial Public Offering [Line Items]
Contribution of capital from parent	$ 0
Net proceeds from IPO		$ 0
Limited Partner | Columbia Energy Group
Initial Public Offering [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest		84.30%

Initial Public Offering (Schedu

Initial Public Offering (Schedule of Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest) (Details) - USD ($) $ in Millions	2 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016
Initial Public Offering [Line Items]
Net Income (Loss) Allocated to Limited Partners	$ 13.3	$ 27.3
Noncontrolling Interest, Increase from Subsidiary Equity Issuance	0
Change from net income attributable to the Partnership and transfers to noncontrolling interest	(411.1)	27.3
Noncontrolling Interest
Initial Public Offering [Line Items]
Noncontrolling Interest, Increase from Subsidiary Equity Issuance	$ (424.4)	$ 0

Net Income Per Limited Partne46

Net Income Per Limited Partner Unit (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	May. 02, 2016	Mar. 31, 2016
Subsequent Event [Member]
Schedule Of Earnings Per Unit [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	$ 18.9
Distribution Made to Limited Partner, Distributions Declared, Per Unit	$ 0.1875
Distribution Made to Limited Partner, Distribution Date	May 20, 2016
Distribution Made to Limited Partner, Date of Record	May 13, 2016
Minimum
Schedule Of Earnings Per Unit [Line Items]
Distribution Made to Limited Partner, Distributions Paid, Per Unit		$ 0.1675
Minimum | Annualized
Schedule Of Earnings Per Unit [Line Items]
Distribution Made to Limited Partner, Distributions Paid, Per Unit		$ 0.67

Net Income Per Limited Partne47

Net Income Per Limited Partner Unit (Schedule of Net Income Per Limited Partner Unit) (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	2 Months Ended		3 Months Ended
	Mar. 31, 2015		Mar. 31, 2016
Schedule Of Earnings Per Unit [Line Items]
Partners' Capital Account, Distributions	$ 0		$ 18.9
Undistributed Earnings, Basic	13.3	[1]	8.4
Net Income (Loss) Allocated to Limited Partners	$ 13.3		$ 27.3
Weighted Average Number of Shares Outstanding, Basic and Diluted	100.6		100.6
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13		$ 0.25
Incentive Distribution Rights [Member]
Schedule Of Earnings Per Unit [Line Items]
Incentive Distribution, Distribution	$ 0		$ 0
Undistributed Earnings, Basic	0	[1]	2.3
Net Income (Loss) Allocated to Limited Partners	0		2.3
Subordinated Units
Schedule Of Earnings Per Unit [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	0		8.8
Undistributed Earnings, Basic	6.2	[1]	2.8
Net Income (Loss) Allocated to Limited Partners	$ 6.2		$ 11.6
Weighted Average Number of Shares Outstanding, Basic and Diluted	46.8		46.8
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13		$ 0.25
Common Units
Schedule Of Earnings Per Unit [Line Items]
Distribution Made to Limited Partner, Cash Distributions Declared	$ 0		$ 10.1
Undistributed Earnings, Basic	7.1	[1]	3.3
Net Income (Loss) Allocated to Limited Partners	$ 7.1		$ 13.4
Weighted Average Number of Shares Outstanding, Basic and Diluted	53.8		53.8
Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Basic and Diluted, Net of Tax	$ 0.13		$ 0.25
[1]	Net income attributable to limited partners and in excess of distribution is for the period subsequent to the IPO.

Transactions With Affiliates (N

Transactions With Affiliates (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015	Dec. 05, 2014
Related Party Transaction [Line Items]
Interest Expense, Long-term Debt	$ 7.7	$ 12.2
Allowance for Funds Used During Construction, Capitalized Interest	0.7	1
Interest Expense, Short-term Borrowings	0.2	$ 0.2
Accounts receivable	122.6		$ 149.4
Line of Credit Facility, Maximum Borrowing Capacity	2,600
Default Provision Floor	50
Short-term borrowings-affiliated	348.8		42.1
Distribution to Parent	108.9
Short-term Debt	15		15
Transportation and Storage Services
Related Party Transaction [Line Items]
Accounts receivable	$ 7		8.9
Money Pool
Related Party Transaction [Line Items]
Short-term Debt, Weighted Average Interest Rate	0.54%	1.07%
Accounts receivable	$ 115.6		$ 140.5
Line of Credit Facility, Maximum Borrowing Capacity	750
Revolving Credit Facility
Related Party Transaction [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	500			$ 1,500
Notes Due 2020
Related Party Transaction [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,300
Debt Instrument, Interest Rate, Stated Percentage	4.70%
Debt Instrument, Maturity Date	Dec. 31, 2020
Columbia OpCo
Related Party Transaction [Line Items]
Reimbursement of Preformation Capital		$ 500

Transactions With Affiliates (S

Transactions With Affiliates (Schedule of Affiliated Transactions) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Related Party Transaction [Line Items]
Transportation revenues	$ 0	$ 28.7
Storage revenues	0	13.3
Other revenues	0	0.1
Operation and maintenance	42.4	36.1
Interest expense	7.2	11.4
Interest income	0.1	$ 1
Accounts receivable	122.6		$ 149.4
Short-term borrowings	348.8		42.1
Accounts payable	22.6		86.3
Long-term debt	$ 630.9		$ 630.9

Transactions With Affiliates 50

Transactions With Affiliates (Schedule of Long-term Debt) (Details) - Notes Due 2020 - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Dec. 9, 2013
Debt Instrument, Interest Rate, Stated Percentage	4.70%
Debt Instrument, Maturity Date	Dec. 31, 2020
Long-term Debt	$ 630.9	$ 630.9

Short-Term Borrowings (Narrativ

Short-Term Borrowings (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)$ / shares	Dec. 31, 2015USD ($)	Dec. 05, 2014USD ($)
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,600
Default Provision Floor	50
Letters of Credit
Short-term Debt [Line Items]
Letters of Credit Outstanding, Amount	0	$ 0
Revolving Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Amount Outstanding	$ 15	$ 15
Federal Funds Effective Swap Rate
Short-term Debt [Line Items]
Basis Spread on Variable Rate	0.50%
London Interbank Offered Rate (LIBOR)
Short-term Debt [Line Items]
Basis Spread on Variable Rate	1.00%
Minimum
Short-term Debt [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.125%
Distribution Made to Limited Partner, Distributions Paid, Per Unit | $ / shares	$ 0.1675
Minimum | Federal Funds Effective Swap Rate
Short-term Debt [Line Items]
Margin Rate	0.00%
Minimum | London Interbank Offered Rate (LIBOR)
Short-term Debt [Line Items]
Margin Rate	0.00%
Minimum | Eurodollar
Short-term Debt [Line Items]
Margin Rate	1.00%
Minimum | Period 1
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5.50
Minimum | Period 2
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5
Minimum | Acquisition Period
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5.50
Maximum
Short-term Debt [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.35%
Maximum | Federal Funds Effective Swap Rate
Short-term Debt [Line Items]
Margin Rate	0.65%
Maximum | London Interbank Offered Rate (LIBOR)
Short-term Debt [Line Items]
Margin Rate	0.65%
Maximum | Eurodollar
Short-term Debt [Line Items]
Margin Rate	1.65%
Maximum | Period 1
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Maximum | Period 2
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Maximum | Acquisition Period
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Revolving Credit Facility
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 500		$ 1,500
Letters of Credit
Short-term Debt [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 50

Short-Term Borrowings (Schedule

Short-Term Borrowings (Schedule of Short-Term Borrowings) (Details) - Revolving Credit Facility - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Short-term Debt [Line Items]
Credit facilities borrowings	$ 15	$ 15
Short-term Debt, Weighted Average Interest Rate	1.50%	1.28%

Gain On Sale Of Assets (Narrati

Gain On Sale Of Assets (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015	Dec. 31, 2015
Gain On Sale of Assets [Abstract]
Gain on Conveyances	$ 2.6	$ 5.3
Deferred Gains On Conveyances	$ 5.5		$ 8.1

Goodwill (Narrative) (Details)

Goodwill (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Goodwill [Abstract]
Goodwill	$ 1,975.5	$ 1,975.5

Asset Retirement Obligations (C

Asset Retirement Obligations (Changes In Company's Liability For Asset Retirement Obligations) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Asset Retirement Obligation [Abstract]
Beginning Balance		$ 25.3	$ 23.2
Noncontributed net parent investment adjustments	[1]	0	(0.4)
Accretion expense		0.3	0.3
Additions		0	0
Settlements		0	0
Change in estimated cash flows		(0.9)	0
Ending Balance		$ 24.7	$ 23.1
[1]	Reflects the removal of amounts related to Crossroads Pipeline Company, which was included in the Predecessor but was not contributed to the Partnership.

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Jan. 01, 2016	Mar. 31, 2016	Feb. 01, 2016
Regulatory Assets and Liabilities Disclosure [Abstract]
Expected Modernization Investment	$ 300
Modernization Program Recovery			$ 320
Annual Capital Cost Recovery Mechanism Extension Limit		$ 1,100

Equity Method Investments Sched

Equity Method Investments Schedule of Equity Method Investments (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Feb. 11, 2015	Mar. 31, 2016	Mar. 31, 2015
Schedule of Equity Method Investments [Line Items]
Contributions to equity investees	$ 1,217.3
Millennium Pipeline
Schedule of Equity Method Investments [Line Items]
Contributions to equity investees		$ 1.9	$ 0
Distributions of earnings from equity investees		15.2	16.6
Hardy Storage
Schedule of Equity Method Investments [Line Items]
Contributions to equity investees		0	0
Distributions of earnings from equity investees		0.7	0.5
Pennant
Schedule of Equity Method Investments [Line Items]
Contributions to equity investees		0	0
Distributions of earnings from equity investees		3	1.2
Return of capital from equity investees		$ 0.2	$ 1.3

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details)	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Income Taxes [Line Items]
Effective income tax rates	0.00%	15.30%
Federal statutory income tax rate	35.00%	35.00%

Pension And Other Postretirem59

Pension And Other Postretirement Benefits (Components Of The Plans' Net Periodic Benefits Cost) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1.3	$ 1.3
Interest cost	3.2	3.1
Expected return on assets	(5.5)	(6.1)
Amortization of prior service credit	(0.2)	(0.2)
Recognized actuarial loss	2.5	2
Total Net Periodic Benefits Cost	1.3	0.1
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0.2	0.3
Interest cost	1	1
Expected return on assets	(3.8)	(4.3)
Amortization of prior service credit	0	0
Recognized actuarial loss	0	0
Total Net Periodic Benefits Cost	$ (2.6)	$ (3)

Fair Value (Carrying Amount And

Fair Value (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term debt	$ 630.9	$ 630.9
Long-term debt-affiliated, Estimated Fair Value	$ 652.8	$ 630.9

Other Commitments And Conting61

Other Commitments And Contingencies (Narrative) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2016USD ($)	Dec. 31, 2015USD ($)	Dec. 05, 2014USD ($)
Other Commitments And Contingencies [Line Items]
Guarantees	$ 2,768.1
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,600
Ozone Level Maximum	70 ppb
Percentage Reduction in Methane Emissions	95.00%
Hours of Operation	26,000
Replacement Years	3 years
Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Commercial Paper	$ 0
Line of Credit Facility Used For Credit Support for Subsidiaries	750
Line of Credit Facility Used For Corporate Purposes	750
Revolving Credit Facility
Other Commitments And Contingencies [Line Items]
Credit facilities borrowings	15	$ 15
Revolving Credit Facility | Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Credit facilities borrowings	0
Letters of Credit
Other Commitments And Contingencies [Line Items]
Letters of Credit Outstanding, Amount	0	$ 0
Letters of Credit | Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Letters of Credit Outstanding, Amount	18.1
Commercial Paper | Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,000
Revolving Credit Facility
Other Commitments And Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	500		$ 1,500
Revolving Credit Facility | Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	1,500
Letters of Credit
Other Commitments And Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	50
Letters of Credit | Columbia Pipeline Group
Other Commitments And Contingencies [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	250
Guarantee of Indebtedness of Others
Other Commitments And Contingencies [Line Items]
Guarantees	2,750
Letters of Credit
Other Commitments And Contingencies [Line Items]
Guarantees	$ 18.1

Other Commitments And Conting62

Other Commitments And Contingencies (Existence and Expiration of Commercial Commitments) (Details) $ in Millions	Mar. 31, 2016USD ($)
Other Commitments and Contingencies [Line Items]
2,016	$ 18.1
2,017	0
2,018	500
2,019	0
2,020	750
After	1,500
Total	2,768.1
Guarantee of Indebtedness of Others
Other Commitments and Contingencies [Line Items]
2,016	0
2,017	0
2,018	500
2,019	0
2,020	750
After	1,500
Total	2,750
Letters of Credit
Other Commitments and Contingencies [Line Items]
2,016	18.1
2,017	0
2,018	0
2,019	0
2,020	0
After	0
Total	$ 18.1

Accumulated Other Comprehensi63

Accumulated Other Comprehensive Loss (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Loss [Line Items]
Other Comprehensive Income Unrecognized Gain Loss On Derivatives Arising During Period Before Tax	$ 24.8	$ 25
Millennium Pipeline
Accumulated Other Comprehensive Loss [Line Items]
Unrealized loss, amortization period	15 years
Debt Instrument, Maturity Date	Jun. 1, 2025

Accumulated Other Comprehensi64

Accumulated Other Comprehensive Loss (Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions		1 Months Ended		2 Months Ended		3 Months Ended
		Feb. 11, 2015		Mar. 31, 2015		Mar. 31, 2016		Mar. 31, 2015
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		$ (16.7)	[1]			$ (4)	[2]	$ (16.7)	[1]
Predecessor net tax liabilities not assumed by Columbia OpCo		1,222.2
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						0	[2]	0	[1]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[3]					0.5	[2]	0.1	[1]
Other Comprehensive Income (Loss), Net of Tax		0.1		$ 0.1		0.5	[2]	0.1	[1]
Ending Balance				(4.2)	[1]	(3.9)	[2]	(4.2)	[1]
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(16.6)	[1]			(3.9)	[2]	(16.6)	[1]
Predecessor net tax liabilities not assumed by Columbia OpCo	[1],[4]							(10.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						0	[2]	0	[1]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[3]					0.5	[2]	0.1	[1]
Other Comprehensive Income (Loss), Net of Tax						0.5	[2]	0.1	[1]
Ending Balance				(4.1)	[1]	(3.8)	[2]	(4.1)	[1]
Accumulated Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance		(0.1)	[1]			(0.1)	[2]	(0.1)	[1]
Predecessor net tax liabilities not assumed by Columbia OpCo	[1],[4]							(0.1)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax						0	[2]	0	[1]
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[3]					0	[2]	0	[1]
Other Comprehensive Income (Loss), Net of Tax						0	[2]	0	[1]
Ending Balance				(0.1)	[1]	(0.1)	[2]	(0.1)	[1]
Accumulated Net Gain (Loss) from Cash Flow Hedges Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax						0.4	[2]	(22.6)	[1]
Accumulated Defined Benefit Plans Adjustment Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax						0	[2]	(0.1)	[1]
AOCI Attributable to Noncontrolling Interest
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax						0.4	[2]	(22.7)	[1]
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Line Items]
Predecessor net tax liabilities not assumed by Columbia OpCo		(10.3)						$ (10.3)	[1],[4]
Other Comprehensive Income (Loss), Net of Tax		$ 0.1		$ 0		$ 0.1
[1]	All amounts prior to the IPO are net of tax. Amounts in parentheses indicate debits.
[2]	Amounts in parentheses indicate debits.
[3]	Includes amounts allocated to noncontrolling interest.
[4]	Reflects the non-cash elimination of all historical current and deferred income taxes other than Tennessee state income taxes that will continue to be borne by the Partnership post-IPO.

Other, Net (Schedule of Other,

Other, Net (Schedule of Other, Net) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Other Nonoperating Income (Expense) [Abstract]
AFUDC Equity	$ 6.1	$ 3.5
Miscellaneous	0	0.8
Total Other, net	$ 6.1	$ 4.3

Supplemental Cash Flow Inform66

Supplemental Cash Flow Information (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Supplemental Cash Flow [Line Items]
Capital expenditures included in current liabilities	[1]	$ 119.2	$ 98.8
Cash paid for interest, net of interest capitalized amounts		$ 7.5	$ 15.6
[1]	Capital expenditures included in current liabilities is comprised of "Accrued capital expenditures" and certain other amounts included within "Accounts payable" on the Condensed Consolidated Balance Sheets (unaudited).

Concentration Of Credit Risk (N

Concentration Of Credit Risk (Narrative) (Details)	3 Months Ended
	Mar. 31, 2016
Concentration Risk [Line Items]
Concentration Risk, Benchmark Description	greater than 10% of total operating revenues

Concentration of Credit Risk (S

Concentration of Credit Risk (Schedule of Concentration Of Credit Risk) (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Concentration Risk [Line Items]
Revenues		$ 363.5	$ 339.2
Credit Concentration Risk
Concentration Risk [Line Items]
Revenues	[1]	$ 50.4	$ 48.9
Concentration Risk, Percentage	[1]	13.90%	14.40%
[1]	Represents the gross amount of revenue contracted for with Columbia Gas of Ohio and, therefore, subject to risk at the loss of this customer. Columbia Gas of Ohio has entered into certain capacity release arrangements with third parties which ultimately can decrease the net revenue amount the Partnership receives from Columbia Gas of Ohio in any given period.

Subsequent Event (Narrative) (D

Subsequent Event (Narrative) (Details) - Subsequent Event [Member] $ / shares in Units, $ in Millions	May. 02, 2016USD ($)$ / shares
Subsequent Event [Line Items]
Distribution Made to Limited Partner, Distributions Declared, Per Unit | $ / shares	$ 0.1875
Distribution Made to Limited Partner, Cash Distributions Declared | $	$ 18.9
Distribution Made to Limited Partner, Distribution Date	May 20, 2016
Distribution Made to Limited Partner, Date of Record	May 13, 2016