Columbia Pipeline (CPGX) 10-Q 3 Nov 15 2015 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2015	Oct. 30, 2015
Document Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2015
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	Q3
Entity Registrant Name	COLUMBIA PIPELINE GROUP, INC./DE
Entity Central Index Key	1,629,995
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Units Outstanding		317,616,350

Statements of Consolidated Bala

Statements of Consolidated Balance Sheets - USD ($) $ in Millions		Sep. 30, 2015	Dec. 31, 2014
Current Assets
Cash and cash equivalents		$ 63.8	$ 0.5
Accounts receivable (less reserve of $0.6 and $0.6, respectively)		133.1	149.4
Accounts receivable-affiliated		0	180
Materials and supplies, at average cost		26	24.9
Exchange gas receivable		24	34.8
Regulatory assets		5.5	6.1
Deferred property taxes		15.5	48.9
Deferred income taxes		50	60
Prepayments and other		50	14.7
Total Current Assets		367.9	519.3
Investments
Unconsolidated affiliates		435.6	444.3
Other investments		15.5	2.7
Total Investments		451.1	447
Property, Plant and Equipment
Property, plant and equipment		8,865.6	7,935.4
Accumulated depreciation and amortization		(3,007.7)	(2,976.8)
Net Property, Plant and Equipment		5,857.9	4,958.6
Other Noncurrent Assets
Regulatory assets		154.1	151.9
Goodwill		1,975.5	1,975.5
Postretirement and postemployment benefits assets		120.1	90
Deferred charges and other		37	15.2
Total Other Noncurrent Assets		2,286.7	2,232.6
Total Assets		8,963.6	8,157.5
Current Liabilities
Current portion of long-term debt-affiliated		0	115.9
Short-term borrowings		245	0
Short-term borrowings-affiliated		0	252.5
Accounts payable		82.9	56
Accounts payable-affiliated		0	53.6
Dividends payable		39.7	0
Customer deposits		17	13.4
Taxes accrued		70.6	103.2
Interest accrued		40.4	0
Exchange gas payable		24.1	34.7
Deferred revenue		13.9	22.5
Regulatory liabilities		9.1	1.3
Accrued capital expenditures		197.2	61.1
Other accruals		111.6	70
Total Current Liabilities		851.5	784.2
Noncurrent Liabilities
Long-term debt		2,746	0
Long-term debt-affiliated		0	1,472.8
Deferred income taxes		1,337.1	1,255.7
Accrued liability for postretirement and postemployment benefits		49.5	53
Regulatory liabilities		317.4	295.7
Asset retirement obligations		22.9	23.2
Other noncurrent liabilities		89.6	96.6
Total Noncurrent Liabilities		4,562.5	3,197
Total Liabilities		5,414	3,981.2
Equity
Common stock, $0.01 par value, 2,000,000,000 shares authorized; 317,616,350 and no shares outstanding, respectively		3.2	0
Additional paid-in capital		2,634.9	0
Accumulated deficit		(16.5)	0
Net parent investment		0	4,210.8
Accumulated other comprehensive loss	[1]	(25.3)	(34.5)
Total CPG Equity		2,596.3	4,176.3
Noncontrolling Interest		953.3	0
Total Equity		3,549.6	4,176.3
Total Liabilities and Equity		$ 8,963.6	$ 8,157.5
[1]	All amounts are net of tax. Amounts in parentheses indicate debits.

Statements of Consolidated Bal3

Statements of Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Statement of Financial Position [Abstract]
Accounts receivable less reserve	$ 0.6	$ 0.6
Common Stock, Par or Stated Value Per Share	$ 0.01
Common Stock, Shares Authorized	2,000,000,000
Common Stock, Shares, Outstanding	317,616,350	0

Statements of Consolidated Oper

Statements of Consolidated Operations - USD ($) shares in Millions, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Operating Revenues
Transportation revenues	$ 266.2	$ 236	$ 752.4	$ 743.4
Transportation revenues-affiliated	0	18.8	47.5	66.2
Storage revenues	49.5	35.9	122.3	108.2
Storage revenues-affiliated	0	13.2	26.2	40.1
Other revenues	5.2	14.1	28.6	49.4
Total Operating Revenues	320.9	318	977	1,007.3
Operating Expenses
Operation and maintenance	186.5	162.6	456	475.4
Operation and maintenance-affiliated	0	32.1	52.9	89.9
Depreciation and amortization	35	29.3	101.4	87.9
Gain on sale of assets and impairment, net	(38.4)	(3)	(50.2)	(20.8)
Property and other taxes	17.3	14.5	55.5	50.3
Total Operating Expenses	200.4	235.5	615.6	682.7
Equity Earnings in Unconsolidated Affiliates	15.4	12	44.5	32.9
Operating Income	135.9	94.5	405.9	357.5
Other Income (Deductions)
Interest expense	(29.4)	0	(42.3)	0
Interest expense-affiliated	0	(14.4)	(29.3)	(39.1)
Other, net	6.7	3.6	16.6	8.2
Total Other Deductions, net	(22.7)	(10.8)	(55)	(30.9)
Income from Continuing Operations before Income Taxes	113.2	83.7	350.9	326.6
Income Taxes	38.3	30	118.8	120.5
Income from Continuing Operations	74.9	53.7	232.1	206.1
Loss from Discontinued Operations-net of taxes	(0.1)	(0.1)	(0.4)	(0.6)
Net Income	74.8	53.6	231.7	205.5
Less: Net income attributable to noncontrolling interest	11.8		27.9
Net income attributable to CPG	63	53.6	203.8	205.5
Amounts Attributable to CPG
Income from continuing operations	63.1	53.7	204.2	206.1
Loss from Discontinued Operations-net of taxes	(0.1)	(0.1)	(0.4)	(0.6)
Net income attributable to CPG	$ 63	$ 53.6	$ 203.8	$ 205.5
Basic Earnings Per Share
Continuing operations	$ 0.20	$ 0.17	$ 0.64	$ 0.65
Discontinued operations	0	0	0	0
Basic Earnings Per Share	0.20	0.17	0.64	0.65
Diluted Earnings Per Share
Continuing Operations	0.20	0.17	0.64	0.65
Discontinued Operations	0	0	0	0
Diluted Earnings Per Share	$ 0.20	$ 0.17	$ 0.64	$ 0.65
Basic Average Common Shares Outstanding	317.6	317.6	317.6	317.6
Diluted Average Common Shares	318.4	317.6	318.4	317.6
Dividends Declared Per Common Share	$ 0.25	$ 0	$ 0.25	$ 0

Statements of Consolidated Comp

Statements of Consolidated Comprehensive Income - USD ($) $ in Millions		3 Months Ended			9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014	Sep. 30, 2015		Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Net Income		$ 74.8		$ 53.6	$ 231.7		$ 205.5
Net unrealized gain (loss) on cash flow hedges	[1]	(0.7)		0.3	(0.2)		0.8
Unrecognized pension and OPEB (costs) benefit	[3]	(0.1)	[2]	(0.2)	7.2	[2]	(0.4)
Total other comprehensive income	[4]	(0.8)		0.1	7		0.4
Total comprehensive income		74		53.7	238.7		205.9
Less: Comprehensive Income-noncontrolling interest		11.8		0	27.9		0
Comprehensive Income-controlling interests		$ 62.2		$ 53.7	$ 210.8		$ 205.9
[1]	Net unrealized gain (loss) on derivatives qualifying as cash flow hedges, net of $1.1 million and $0.2 million tax expense for the three months ended September 30, 2015 and 2014, respectively, and $1.4 million and $0.5 million tax expense for the nine months ended September 30, 2015 and 2014, respectively.
[2]	Unrecognized pension and OPEB costs are primarily related to pension and OPEB remeasurement recorded during 2015.
[3]	Unrecognized pension and other postretirement benefit (“OPEB”) costs, net of $0.1 million tax benefit for the three months ended September 30, 2015 and 2014, and $0.1 million and $0.3 million tax benefit for the nine months ended September 30, 2015 and 2014, respectively.
[4]	All amounts are net of tax. Amounts in parentheses indicate debits.

Statements of Consolidated Com6

Statements of Consolidated Comprehensive Income (Parenthetical) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Statement of Comprehensive Income [Abstract]
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	$ 1.1	$ 0.2	$ 1.4	$ 0.5
Other Comprehensive (Income) Loss, Pension and Other Postretirement Benefit Plans, Tax	$ 0.1	$ 0.1	$ 0.1	$ 0.3

Statements of Consolidated Cash

Statements of Consolidated Cash Flows - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Operating Activities
Net Income	$ 231.7	$ 205.5
Adjustments to Reconcile Net Income to Net Cash from Continuing Operations:
Depreciation and amortization	101.4	87.9
Deferred income taxes and investment tax credits	77.7	78.8
Deferred revenue	0.4	2.2
Equity-based compensation expense and profit sharing contribution	4.4	4.4
Gain on sale of assets and impairment, net	(50.2)	(20.8)
Income from unconsolidated affiliates	(44.5)	(32.9)
Loss from discontinued operations-net of taxes	0.4	0.6
Amortization of debt related costs	1.8	0
AFUDC equity	(15)	(8.2)
Distributions of earnings received from equity investees	44.1	27.6
Changes in Assets and Liabilities:
Accounts receivable	1.6	2.3
Accounts receivable-affiliated	34.7	15.7
Accounts payable	20.6	(0.3)
Accounts payable-affiliated	(53.6)	5.8
Customer deposits	(23.8)	75.2
Taxes accrued	(27.6)	(40.2)
Interest accrued	40.3	0
Exchange gas receivable/payable	0.1	3.5
Other accruals	37.1	0
Prepayments and other current assets	9.5	26.8
Regulatory assets/liabilities	38.2	35.3
Postretirement and postemployment benefits	(26)	(19.1)
Deferred charges and other noncurrent assets	3.8	(4)
Other noncurrent liabilities	7.2	0.7
Net Operating Activities from Continuing Operations	414.3	446.8
Net Operating Activities used for Discontinued Operations	(0.1)	(1.3)
Net Cash Flows from Operating Activities	414.2	445.5
Investing Activities
Capital expenditures	(833)	(527.4)
Insurance recoveries	2.1	6.8
Change in short-term lendings-affiliated	145.5	(33.6)
Proceeds from disposition of assets	53.3	5.9
Contributions to equity investees	(1.4)	(63.8)
Distributions from equity investees	15.1	0
Other investing activities	(24.2)	(5.5)
Net Cash Flows used for Investing Activities	(642.6)	(617.6)
Financing Activities
Change in short-term borrowings	245	0
Change in short-term borrowings-affiliated	(252.5)	(378.9)
Issuance of long-term debt	2,745.9	0
Debt related costs	(23.6)	0
Issuance of long-term debt-affiliated	1,217.3	551
Payments of long-term debt-affiliated, including current portion	(2,806)	0
Proceeds from the issuance of common units, net of offering costs	1,168.4	0
Distribution of IPO proceeds to parent	(500)	0
Distribution to parent	(1,450)	0
Distribution to noncontrolling interest	(13.9)	0
Dividends paid - common stock	(39.7)	0
Transfer from parent	0.8	0
Net Cash Flows from Financing Activities	291.7	172.1
Change in cash and cash equivalents	63.3	0
Cash and cash equivalents at beginning of period	0.5	0.4
Cash and Cash Equivalents at End of Period	$ 63.8	$ 0.4

Statements of Consolidated Equi

Statements of Consolidated Equity - 9 months ended Sep. 30, 2015 - USD ($) shares in Millions, $ in Millions		Total		Common Stock	Additional Paid-in Capital	Accumulated Deficit	Net Parent Investment	Accumulated Other Comprehensive Income (Loss)	Noncontrolling Interest
Beginning Balance at Dec. 31, 2014		$ 4,176.3		$ 0	$ 0	$ 0	$ 4,210.8	$ (34.5)	$ 0
Net Income		231.7		0	0	63		0
Other Comprehensive Income (Loss), Net of Tax		7	[1]	0	0	0	0	7	0
Allocation of Accumulated Other Comprehensive Loss To Noncontrolling Interest		0		0	0	0	0	2.2	(2.2)
Issuance of common units of CPPL		1,168.4		0	0	0	0	0	1,168.4
Distribution of IPO proceeds to NiSource		(500)		0	0	0	(500)	0	0
Distribution to NiSource		(1,450)		0	0	0	(1,450)	0	0
Sale of interest in Columbia OpCo to CPPL	[2]	0		0	0	0	227.1	0	(227.1)
Distribution of IPO proceeds to NiSource		(13.9)		0	0	0	0	0	(13.9)
Net transfers from NiSource		6.3		0	0	0	6.3	0	0
Reclassification of net parent investment to additional paid-in capital		0		0	2,635	0	(2,635)	0	0
Issuance of common stock at Separation		0		3.2	(3.2)	0	0	0	0
Net transfers from NiSource		$ 1.4		$ 0	$ 1.2	$ 0	$ 0	$ 0	$ 0.2
Long-term incentive plan		1.9		0	1.9	0	0	0	0
Common stock dividends		$ (79.5)		$ 0	$ 0	$ (79.5)	$ 0	$ 0	$ 0
Ending Balance at Sep. 30, 2015		$ 3,549.6		$ 3.2	$ 2,634.9	$ (16.5)	$ 0	$ (25.3)	$ 953.3
[1]	All amounts are net of tax. Amounts in parentheses indicate debits.
[2]	Represents the sale of an additional 8.4% limited partner interest in Columbia OpCo, recorded at the historical carrying value of Columbia OpCo’s net assets after giving effect to the $1,168.4 million equity contribution. This decreases the noncontrolling interest by the same amount it increases the net parent investment because CPPL’s purchase price for its additional 8.4% interest in Columbia OpCo exceeded book value.

Statements of Consolidated Equ9

Statements of Consolidated Equity (Parenthetical) - USD ($) $ in Millions	8 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Issuance of common units of CPPL	$ 1,168.4	$ 1,168.4
Columbia OpCo
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Additional Ownership Interest	8.40%

Basis of Accounting Presentatio

Basis of Accounting Presentation	9 Months Ended
	Sep. 30, 2015
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Basis of Accounting Presentation	Basis of Accounting Presentation Columbia Pipeline Group, Inc. ("CPG") is a growth-oriented Delaware corporation formed by NiSource Inc. ("NiSource") on September 26, 2014 to own, operate and develop a portfolio of pipelines, storage and related midstream assets. 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. CPG indirectly owns the general partner of CPPL and all of CPPL’s subordinated units and incentive distribution rights. CPG did not have any material assets or liabilities as a separate corporate entity until the contribution of CEG from NiSource on February 11, 2015. As a result of this contribution, the financial statements for periods as of and subsequent to September 26, 2014 reflect the consolidated financial position, results of operations and cash flows for CPG. CPG is engaged in regulated 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 a tariff at rates subject to FERC approval. Separation. On June 2, 2015, NiSource announced that its board of directors approved the separation of CPG from NiSource (the “Separation”) through the distribution of CPG common stock to holders of NiSource common stock as of June 19, 2015 (the “Record Date”). On July 1, 2015, NiSource distributed, pursuant to an effective registration statement on Form 10, 317.6 million shares, one share of CPG common stock for every one share of NiSource common stock held by NiSource shareholders on the Record Date. As of July 1, 2015, CPG is an independent, publicly traded company, and NiSource does not retain any ownership interest in CPG. CPG's common stock began trading "regular-way" under the ticker symbol "CPGX" on the NYSE on July 2, 2015. In connection with the Separation, CPG completed the following transactions: • In May 2015, CPG completed its private placement of senior notes and received proceeds of approximately $2,722.3 million . CPG utilized a portion of the proceeds to repay approximately $1,087.3 million of intercompany debt and short-term borrowings, including, net amounts due from the money pool between CPG and NiSource Finance Corp. ("NiSource Finance"); • CPG further utilized the proceeds from the senior notes to make a cash distribution of approximately $1,450.0 million to NiSource; and • Accounts related to NiSource and its subsidiaries, including accounts receivable and accounts payable, were reclassified from affiliated to non-affiliated. Agreements with NiSource following the Separation . CPG entered into the Separation and Distribution Agreement and several other agreements with NiSource to effect the Separation and provide a framework for CPG’s relationship with NiSource, and its subsidiaries, after the Separation. The Separation and Distribution Agreement contains many of the key provisions related to CPG’s separation from NiSource and the distribution of CPG’s shares of common stock to NiSource’s shareholders, including cross-indemnities between CPG and NiSource. In general, NiSource has agreed to indemnify CPG for any liabilities relating to NiSource's business and CPG has agreed to indemnify NiSource for any liabilities relating to CPG's business. In addition to the Separation and Distribution Agreement, CPG entered into the following agreements with NiSource related to the Separation: • Tax Allocation Agreement - Provides for the respective rights, responsibilities, and obligations of NiSource and CPG with respect to tax liabilities and benefits, tax attributes, the preparation and filing of tax returns, tax contests, and certain other matters regarding taxes. • Employee Matters Agreement - Provides for the respective obligations to employees and former employees who are or were associated with CPG (including those employees who transferred employment from NiSource to CPG prior to the Separation) and for other employment and employee benefits matters. • Transition Services Agreement - Provides for the provision of certain transitional services by NiSource to CPG, and vice versa. The services may include the provision of administrative and other services identified by the parties. The charge for these services is expected to be based on actual costs incurred by the party rendering the services without profit. The Condensed Consolidated Financial Statements (unaudited) have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission. 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 CPG believes that the disclosures made are adequate to make the information not misleading. These financial statements should be read in conjunction with the Company’s audited consolidated financial statements for the year ended December 31, 2014. These financial statements reflect all normal recurring adjustments that are, in the opinion of management, necessary to fairly present CPG’s results of operations and financial position. Amounts reported in the Condensed Statements of Consolidated Operations (unaudited) are not necessarily indicative of amounts expected for the respective annual periods. CPG’s accompanying Condensed Consolidated Financial Statements (unaudited) have been prepared in accordance with GAAP on the basis of NiSource’s historical ownership of CPG’s assets and its operations. These financial statements include the accounts of the following subsidiaries: Columbia Gas Transmission, Columbia Gulf, Columbia Midstream, CEVCO, CNS Microwave, Crossroads, CPGSC, CEG, Columbia Remainder Corporation, CPP GP LLC, CPPL, OpCo GP, Columbia OpCo and CPG. Also included in the Condensed Consolidated Financial Statements (unaudited) are equity method investments Hardy Storage, Millennium Pipeline, and Pennant. All intercompany transactions and balances have been eliminated.

CPPL Initial Public Offering

CPPL Initial Public Offering	9 Months Ended
	Sep. 30, 2015
Equity [Abstract]
CPPL Initial Public Offering	CPPL Initial Public Offering On December 5, 2007, NiSource formed CPPL (NYSE: CPPL) to own, operate and develop a portfolio of pipelines, storage and related assets. On February 11, 2015 , CPPL completed its offering of 53.8 million common units representing limited partner interests, constituting 53.5% of CPPL's outstanding limited partner interests. CPPL received $1,168.4 million of net proceeds from IPO. Prior and subsequent to the Separation, CPG owns the general partner of CPPL, all of CPPL's subordinated units and incentive distribution rights. The assets of CPPL consist of a 15.7% limited partner interest in Columbia OpCo, which prior to the Separation, consisted of substantially all of NiSource's Columbia Pipeline Group Operations segment. The operations of CPPL are consolidated in CPG’s results. As of September 30, 2015 , the portion of CPPL owned by the public is reflected as a noncontrolling interest in the Condensed Consolidated Financial Statements (unaudited). The table below summarizes the effects of changes in CPG’s ownership interest in Columbia OpCo on equity: Three Months Ended Nine Months Ended (in millions) 2015 2015 Net income attributable to CPG $ 63.0 $ 203.8 Increase in CPG’s net parent investment for the sale of 8.4% of Columbia OpCo — 227.1 Change from net income attributable to CPG and transfers to noncontrolling interest $ 63.0 $ 430.9

Recent Accounting Pronouncement

Recent Accounting Pronouncements	9 Months Ended
	Sep. 30, 2015
New Accounting Pronouncements and Changes in Accounting Principles [Abstract]
Recent Accounting Pronouncements	Recent Accounting Pronouncements 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. CPG is required to adopt ASU 2015-03 and ASU 2015-15 for periods beginning after December 15, 2015, including interim periods, and the guidance is to be applied retrospectively with early adoption permitted. CPG is currently evaluating the impact the adoption of ASU 2015-03 and ASU 2015-15 will have on the Condensed Consolidated Financial Statements (unaudited) or Notes to Condensed Consolidated Financial Statements (unaudited). 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 a limited basis. CPG is currently evaluating the impact the adoption of ASU 2014-09 and ASU 2015-14 will have on the Condensed Consolidated Financial Statements (unaudited) or Notes to Condensed Consolidated Financial Statements (unaudited). In April 2015, the FASB issued ASU 2015-05, Intangibles - Goodwill and Other-Internal-Use Software (Subtopic 350-40): Customer's Accounting for Fees Paid in a Cloud Computing Arrangement. ASU 2015-05 clarifies guidance on determining whether a cloud computing arrangement contains a software license that should be accounted for as internal-use software. CPG is required to adopt ASU 2015-05 for periods beginning after December 15, 2015, including interim periods, and the guidance is permitted to be applied either (1) prospectively to all agreements entered into or materially modified after the effective date or (2) retrospectively, with early adoption permitted. CPG is currently evaluating the impact the adoption of ASU 2015-05 will have on the Condensed Consolidated Financial Statements (unaudited) or Notes to Condensed Consolidated Financial Statements (unaudited) but does not anticipate that the impact will be material. 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. CPG is required to adopt ASU 2015-02 for periods beginning after December 15, 2015, including interim periods, and the guidance is to be applied retrospectively or using a modified retrospective approach, with early adoption permitted. CPG is currently evaluating the impact the adoption of ASU 2015-02 will have on the Condensed Consolidated Financial Statements (unaudited) or Notes to Condensed Consolidated Financial Statements (unaudited) but does not anticipate that the impact will be material.

Earnings Per Share

Earnings Per Share	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Earnings Per Share [Text Block]	Earnings Per Share Basic earnings per share ("EPS") is based on net income attributable to CPG and is calculated based upon the daily weighted-average number of common shares outstanding during the periods presented. Also, this calculation includes fully vested awards that have not yet been issued as common stock. Diluted EPS includes the above, plus unvested stock awards granted under our compensation plans, but only to the extent these instruments dilute earnings per share. On July 1, 2015, 317.6 million shares of CPG common stock were distributed to NiSource shareholders in conjunction with the Separation. For comparative purposes, and to provide a more meaningful calculation for weighted average shares, CPG has assumed this amount to be outstanding as of the beginning of each period prior to the Separation presented in the calculation of weighted average shares outstanding. The calculation of diluted average common shares is as follows: Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 Basic average common shares outstanding 317.6 317.6 317.6 317.6 Dilutive potential common shares: Shares restricted under stock plans 0.8 — 0.8 — Diluted average common shares 318.4 317.6 318.4 317.6 Dividends. CPG paid a dividend of $0.125 per share to common shareholders on August 20, 2015 . On August 4, 2015, CPG declared a $0.125 per share to common shareholders of record at October 30, 2015 , payable November 20, 2015 .

Transactions with Affiliates

Transactions with Affiliates	9 Months Ended
	Sep. 30, 2015
Related Party Transactions [Abstract]
Transactions with Affiliates	Transactions with Affiliates Prior to the Separation, CPG engaged in transactions with subsidiaries of NiSource, which at that time were deemed to be affiliates of CPG. The Separation occurred on July 1, 2015 and for periods after this date CPG and the subsidiaries of NiSource are no longer affiliates. Transactions with affiliates prior to the Separation are summarized below: Statement of Operations. Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 Transportation revenues $ — $ 18.8 $ 47.5 $ 66.2 Storage revenues — 13.2 26.2 40.1 Other revenues — 0.1 0.2 0.3 Operation and maintenance expense — 32.1 52.9 89.9 Interest expense — 14.4 29.3 39.1 Interest income — 0.2 2.5 0.5 Balance Sheet. (in millions) September 30, 2015 December 31, 2014 Accounts receivable $ — $ 180.0 Current portion of long-term debt — 115.9 Short-term borrowings — 252.5 Accounts payable — 53.6 Long-term debt — 1,472.8 Transportation, Storage and Other Revenues . CPG provides natural gas transportation, storage and other services to subsidiaries of NiSource, former affiliates. Operation and Maintenance Expense . CPG received executive, financial, legal, information technology and other administrative and general services from a former affiliate, NiSource Corporate Services Company ("NiSource Corporate Services"). Expenses incurred as a result of these services consisted of employee compensation and benefits, outside services and other expenses. CPG was 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 . Prior to the private placement of senior notes on May 22, 2015, CPG paid NiSource interest for intercompany long-term debt outstanding. For the three months ended September 30, 2014 , CPG was charged interest for long-term debt of $16.4 million , offset by associated AFUDC of $2.8 million . For the nine months ended September 30, 2015 and 2014 , CPG was charged interest for long-term debt of $31.0 million and $42.5 million , respectively, offset by associated AFUDC of $2.4 million and $6.0 million , respectively. Columbia OpCo and its subsidiaries entered into an intercompany money pool agreement with NiSource Finance, which became effective on the closing date of CPPL’s IPO. Following the Separation, the agreement is 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 CPPL’s IPO, the subsidiaries of CPG participated in a similar money pool agreement with NiSource Finance. Prior to the Separation, NiSource Corporate Services administered the money pools. Prior to the Separation, the cash accounts maintained by the subsidiaries of Columbia OpCo and CPG were 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. The amount of interest expense and income for short-term borrowings was determined by the net position of each subsidiary in the money pool. Subsequent to the Separation, the intercompany money pool balances and related interest expense and income are eliminated as intercompany activity. The money pool weighted-average interest rate at September 30, 2015 and 2014 was 1.21% and 0.68% , respectively. For the three months ended September 30, 2015 and 2014 , the interest expense for short-term borrowings charged was zero and $0.8 million , respectively. For the nine months ended September 30, 2015 and 2014 , the interest expense for short-term borrowings charged was $0.7 million and $2.6 million , respectively. Accounts Receivable . CPG included in accounts receivable amounts due from the money pool discussed above of $145.5 million at December 31, 2014 for subsidiaries in a net deposit position. Also included in the balance at December 31, 2014 are amounts due from subsidiaries of NiSource for transportation and storage services of $34.5 million . Net cash flows related to the money pool receivables, including the receipt of money pool deposits from NiSource at the time of Separation, are included as Investing Activities on the Condensed Statements of Consolidated Cash Flows (unaudited). All other affiliated receivables are included as Operating Activities. Short-term Borrowings . The subsidiaries of CPG entered into an intercompany money pool agreement with NiSource Finance with $750.0 million of reserved borrowing capacity. Following the Separation, the agreement is 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 guarantors and restricted subsidiaries, CEG, OpCo GP and Columbia OpCo are 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 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 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 September 30, 2015 , neither CPG nor its consolidated subsidiaries had any restricted net 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 CPG. CPG’s revolving credit agreement 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 December 31, 2014 of $252.5 million included those subsidiaries of CPG in a net borrower position of the NiSource Finance money pool discussed above. Net cash flows related to Short-term Borrowings, including the repayment of money pool borrowings to NiSource at the time of Separation, are included as Financing Activities on the Condensed Statements of Consolidated Cash Flows (Unaudited). Accounts Payable . The affiliated accounts payable primarily included amounts due for services received from NiSource Corporate Services and interest payable to NiSource Finance. Long-term Debt . CPG’s long-term financing requirements prior to the private placement of senior notes on May 22, 2015 were satisfied through borrowings from NiSource Finance. CPG used a portion of net proceeds from the senior notes to repay approximately $1,087.3 million of intercompany debt and short-term borrowings, net of amounts due from the money pool, between CPG and NiSource Finance. Details of the affiliated long-term debt balance are summarized in the table below: Origination Date Interest Rate Maturity Date September 30, 2015 December 31, 2014 (in millions) November 28, 2005 (1) 5.41 % November 30, 2015 $ — $ 115.9 November 28, 2005 5.45 % November 28, 2016 — 45.3 November 28, 2005 5.92 % November 28, 2025 — 133.5 November 28, 2012 4.63 % November 28, 2032 — 45.0 November 28, 2012 4.94 % November 30, 2037 — 95.0 December 19, 2012 5.16 % December 21, 2037 — 55.0 November 28, 2012 5.26 % November 28, 2042 — 170.0 December 19, 2012 5.49 % December 18, 2042 — 95.0 December 9, 2013 (2) 4.75 % December 31, 2016 — 834.0 Total Long-term Debt $ — $ 1,588.7 (1) The debt balance for the note originating on November 28, 2005 and maturing on November 30, 2015 is included in "Current portion of long-term debt-affiliated" on the Condensed Consolidated Balance Sheets as of December 31, 2014. (2) CPG may borrow at any time from the origination date to the maturity date not to exceed $2.6 billion . The note carries a variable interest rate of prime plus 150 basis points. All funds borrowed on the note are due December 31, 2016 . Dividends to NiSource . Prior to the Separation, CPG distributed $500.0 million of the proceeds from CPPL’s IPO to NiSource as a reimbursement of preformation capital expenditures with respect to the assets contributed to Columbia OpCo and $1,450.0 million of proceeds related to the issuance of senior notes in May 2015. CPG paid no dividends to NiSource in 2014. There were no restrictions on the payment by CPG of dividends to NiSource.

Short-Term Borrowings

Short-Term Borrowings	9 Months Ended
	Sep. 30, 2015
Short-term Debt [Abstract]
Short-Term Borrowings	Short-Term Borrowings CPG Revolving Credit Facility. On December 5, 2014, CPG entered into a $1,500.0 million senior revolving credit facility, of which $250.0 million in letters of credit is available. The revolving credit facility became effective as of the Separation with a termination date of July 2, 2020. CPG expects that $750.0 million of this facility will be utilized as credit support for Columbia OpCo and its subsidiaries and the remaining $750.0 million of this 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. Obligations under the CPG revolving credit facility are unsecured. Loans under the CPG revolving credit facility will bear interest at CPG’s option at either (i) the greatest of (a) the federal funds effective rate plus 0.500 percent , (b) the reference prime rate of JPMorgan Chase Bank, N.A., or (c) the Eurodollar rate which is based on the London Interbank Offered Rate (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. CPG’s revolving credit facility is subject to a facility fee that varies from 0.125 percent to 0.350 percent per annum, according to CPG’s credit rating. Revolving indebtedness under the CPG credit facility will rank equally with all of CPG’s outstanding unsecured and unsubordinated debt. CEG, OpCo GP and Columbia OpCo have each fully guaranteed the CPG credit facility. The CPG revolving credit facility contains 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 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 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 September 30, 2015 , neither CPG nor its consolidated subsidiaries had any restricted net 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 CPG. The CPG 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 . The CPG revolving credit facility also contains certain financial covenants that require CPG to maintain a consolidated total leverage ratio that does not exceed (i) 5.75 to 1.00 for any period of four consecutive fiscal quarters (each, a “test period”) ending December 31, 2015, (ii) 5.50 to 1.00 for any test period ending after December 31, 2015 and on or before December 31, 2017, and (iii) 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 CPG revolving credit facility), the leverage ratio may 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 CPG or any guarantor. As of September 30, 2015 , CPG had $225.0 million in outstanding borrowings and had $18.1 million in letters of credit under the revolving credit facility. CPPL Revolving Credit Facility. On December 5, 2014, CPPL 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 CPPL's 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. CPPL’s obligations under the revolving credit facility are unsecured. The loans thereunder bear interest at CPPL’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 London Interbank Offered Rate (“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 CPPL's credit facility ranks equally with all CPPL’s outstanding unsecured and unsubordinated debt. CPG, CEG, OpCo GP and Columbia OpCo have each fully guaranteed CPPL's credit facility. CPPL’s revolving credit facility contains various covenants and restrictive provisions which, among other things, limit CPPL’s ability and CPPL’s restricted subsidiaries’ ability to incur additional indebtedness, guarantees and/or liens; consolidate, merge or transfer all or substantially all of CPPL’s 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 CPPL’s organizational documents. The restricted payment provision does not prohibit CPPL 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 CPPL revolving credit agreement), and neither CPPL nor any of its restricted subsidiaries has any restrictions on its ability to make distributions under its organizational documents. In particular, in accordance with CPPL's partnership agreement, the general partner has adopted a policy that CPPL will make quarterly cash distributions in amounts equal to at least the minimum quarterly distributions 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 September 30, 2015 , neither CPPL nor its consolidated subsidiaries had any restricted net assets. If CPPL fails to perform the 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. CPPL’s revolving credit facility also contains customary events of default, including cross default provisions that apply to any other indebtedness it may have with an outstanding principal amount in excess of $50.0 million . The revolving credit facility also contains certain financial covenants that require CPPL to maintain a consolidated total leverage ratio that does not exceed (i) 5.75 to 1.00 for the period of four consecutive fiscal quarters (“test period”) ending December 31, 2015, (ii) 5.50 to 1.00 for any test period ending after December 31, 2015 and on or before December 31, 2017, and (iii) 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 CPPL 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 CPPL or any guarantor. As of September 30, 2015 , CPPL had $20.0 million in outstanding borrowings and issued no letters of credit under the revolving credit facility. CPG Commercial Paper Program. On October 5, 2015, CPG 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 . CEG, OpCo GP and Columbia OpCo 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.

Long-Term Debt

Long-Term Debt	9 Months Ended
	Sep. 30, 2015
Debt Instrument [Line Items]
Long-Term Debt	Long-Term Debt Senior notes issuance. On May 22, 2015, CPG issued its private placement of $2,750.0 million in aggregated principal amount of its senior notes, comprised of $500.0 million of 2.45% senior notes due 2018 (the “2018 Notes”), $750.0 million of 3.30% senior notes due 2020 (the “2020 Notes”), $1,000.0 million of 4.50% senior notes due 2025 (the “2025 Notes”) and $500.0 million of 5.80% senior notes due 2045 (the “2045 Notes” and, together with the 2018 Notes, 2020 Notes and 2025 Notes, the “Notes”). The Notes were issued at a discount, for net proceeds of approximately $2,722.3 million after deducting the Initial Purchasers’ discount and estimated offering expenses of CPG. Indenture. The Notes are governed by an Indenture, dated as of May 22, 2015 (the “Indenture”), entered into by CPG and the certain subsidiary guarantors named therein (the "Guarantors") with U.S. Bank National Association, as trustee (the “Trustee”). The initial Guarantors are three subsidiaries of CPG, CEG, Columbia OpCo and OpCo GP. The Notes are fully and unconditionally guaranteed, jointly and severally, on a senior unsecured basis by all of the Guarantors. Each guarantee of CPG’s obligations under the Notes is a direct, unsecured and unsubordinated obligation of the applicable Guarantor and has the same ranking with respect to indebtedness of that Guarantor as the Notes have with respect to CPG’s indebtedness. The guarantees of any Guarantor may be released under certain circumstances. First, if CPG discharges or defeases its obligations with respect to the Notes of any series, 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 the Notes. The Indenture governing the Notes contains covenants that, among other things, limit the ability of CPG and certain of its subsidiaries to incur liens, to enter into sale and lease-back transactions and to enter into mergers, consolidations or transfers of all or substantially all of their assets. The Indenture also contains customary events of default. The 2018 Notes will mature on June 1, 2018 , the 2020 Notes will mature on June 1, 2020 , the 2025 Notes will mature on June 1, 2025 and the 2045 Notes will mature on June 1, 2045 . Interest on the Notes of each series will be payable semi-annually in arrears on June 1 and December 1, commencing on December 1, 2015. Registration Rights Agreement. In connection with the private placement of the Notes, CPG and the Guarantors entered into a Registration Rights Agreement (the “Registration Rights Agreement”) with the Initial Purchasers, pursuant to which CPG and the Guarantors agreed to file, and use their reasonable best efforts to cause to become effective, an exchange offer registration statement with the SEC and to consummate an exchange offer within 360 days after the date of issuance of the Notes pursuant to which holders of each series of the Notes can exchange the Notes issued in the offering for registered notes having the same terms as the Notes. Under certain circumstances set forth in the Registration Rights Agreement, in lieu of a registered exchange offer, CPG and the Guarantors must file, and use reasonable best efforts to cause to become effective, a shelf registration statement for the resale of the Notes. If CPG fails to satisfy these obligations on a timely basis, the annual interest borne by the Notes will be increased by up to 0.50% per annum until the exchange offer is completed or the shelf registration statement is declared effective.

Gain on Sale of Assets

Gain on Sale of Assets	9 Months Ended
	Sep. 30, 2015
Gain On Sale of Assets [Abstract]
Gain on Sale of Assets	Gain on Sale of Assets CPG recognizes gains on conveyances of mineral rights positions into earnings as any obligation associated with conveyance is satisfied. For the three months ended September 30, 2015 and 2014 , gains on conveyances amounted to $36.0 million and $3.0 million , respectively, and are included in "Gain on sale of assets and impairment, net" on the Condensed Statements of Consolidated Operations (unaudited). For the nine months ended September 30, 2015 and 2014 , gains on conveyances amounted to $49.6 million and $20.8 million , respectively, and are included in "Gain on sale of assets and impairment, net" on the Condensed Statements of Consolidated Operations (unaudited). Included in the gains on conveyances is a cash bonus payment of $35.8 million received by CEVCO from CNX Gas Company LLC during the three months ended September 30, 2015 for the lease of Utica Shale and Upper Devonian gas rights in Greene and Washington Counties in Pennsylvania and Marshall and Ohio Counties in West Virginia. As of September 30, 2015 and December 31, 2014 , deferred gains of approximately $10.7 million and $19.6 million , respectively, were deferred pending performance of future obligations and recorded within "Deferred revenue," on the Condensed Consolidated Balance Sheets (unaudited).

Goodwill

Goodwill	9 Months Ended
	Sep. 30, 2015
Goodwill and Intangible Assets Disclosure [Abstract]
Goodwill	Goodwill CPG 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 which have been designated as components and aggregated based on the regulated nature of their operations and similar economic characteristics (e.g., the offering of FERC-regulated pipeline transportation and storage services to LDCs, municipal utilities, direct industrial users, electric power generators and marketers). All of CPG's goodwill relates to NiSource's acquisition of CEG in 2000, which was contributed to CPG prior to the Separation. CPG’s goodwill assets at September 30, 2015 were $1,975.5 million . CPG 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. CPG 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, CPG 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. CPG 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. No such indicators were noted that would require a subsequent goodwill impairment test during the third quarter of 2015 .

Asset Retirement Obligations

Asset Retirement Obligations	9 Months Ended
	Sep. 30, 2015
Asset Retirement Obligation [Abstract]
Asset Retirement Obligations	Asset Retirement Obligations Changes in CPG’s liability for asset retirement obligations for the nine months ended September 30, 2015 and 2014 are presented in the table below: (in millions) 2015 2014 Balance as of January 1, $ 23.2 $ 26.3 Accretion expense 0.9 1.1 Additions 0.4 2.0 Settlements — — Change in estimated cash flows (1.6 ) (0.2 ) Balance as of September 30, $ 22.9 $ 29.2 CPG's 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. CPG 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	9 Months Ended
	Sep. 30, 2015
Regulatory Assets and Liabilities Disclosure [Abstract]
Regulatory Matters	Regulatory Matters Columbia Gas Transmission Customer Settlement. In November 2014, Columbia Gas Transmission commenced the third year of the Columbia Gas Transmission long-term system modernization program. Columbia Gas Transmission expects to place approximately $319 million in modernization investments into service during the year. Recovery of approximately $320 million of investments made in 2014 began on February 1, 2015. 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 Natural Gas Act. 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	9 Months Ended
	Sep. 30, 2015
Equity Method Investments [Abstract]
Equity Method Investments	Equity Method Investments Certain investments of CPG are accounted for under the equity method of accounting. Income and losses from Millennium Pipeline, Hardy Storage and Pennant are reflected in “Equity Earnings in Unconsolidated Affiliates” on the Condensed Statements of Consolidated Operations (unaudited). These investments are integral to CPG’s business. Contributions are made to these equity investees to fund CPG’s share of capital projects. Columbia Gas Transmission contributed $1.4 million to Millennium Pipeline for the three months ended September 30, 2015 and made no contributions for the three months ended September 30, 2014 . Columbia Gas Transmission received $13.3 million and $14.2 million of earnings distributions from Millennium Pipeline during the three months ended September 30, 2015 and 2014 , respectively. Columbia Gas Transmission contributed $1.4 million and $2.6 million to Millennium Pipeline for the nine months ended September 30, 2015 and 2014 , respectively. Columbia Gas Transmission received $37.5 million and $26.1 million of earnings distributions from Millennium Pipeline during the nine months ended September 30, 2015 and 2014 , respectively. No contributions were made to Hardy Storage during the three months ended September 30, 2015 and 2014 . No distributions were received from Hardy Storage during the three months ended September 30, 2015 . CPG received $0.5 million of earnings distributions from Hardy Storage during the three months ended September 30, 2014 . No contributions were made to Hardy Storage during the nine months ended September 30, 2015 and 2014 . CPG received $1.0 million and $1.5 million of earnings distributions from Hardy Storage during the nine months ended September 30, 2015 and 2014 , respectively. No contributions were made to Pennant for the three months ended September 30, 2015 and contributions of $9.0 million were made for the three months ended September 30, 2014 . Columbia Midstream received $2.9 million of earnings distributions and a return of capital of $0.2 million from Pennant during the three months ended September 30, 2015 . No distributions were received from Pennant during the three months ended September 30, 2014 . No contributions were made to Pennant for the nine months ended September 30, 2015 and contributions of $61.2 million were made for the nine months ended September 30, 2014 . Columbia Midstream received $5.6 million of earnings distributions and a return of capital of $2.4 million from Pennant during the nine months ended September 30, 2015 . No distributions were received from Pennant during the nine months ended September 30, 2014 . During the third quarter of 2015 , an additional member joined the Pennant joint venture. The member's initial ownership investment in Pennant is 5.00% , and by funding specified, disproportionate investment amounts for future growth projects, the member can invest directly in the growth of Pennant. Such funding will potentially increase the member's ownership in Pennant up to 33.33% over a defined investment period. As a result of the buy-in, Columbia Midstream received $12.7 million in cash and recorded a gain of $2.9 million , and its ownership interest in Pennant decreased from 50.00% to 47.50% .

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2015
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes CPG’s interim effective tax rates reflect the estimated annual effective tax rates for 2015 and 2014 , adjusted for tax expense associated with certain discrete items. The effective tax rates for the three months ended September 30, 2015 and 2014 were 33.8% and 35.8% , respectively. The effective tax rates for the nine months ended September 30, 2015 and 2014 were 33.9% and 36.9% , respectively. The effective tax rate for 2015 differs from the Federal tax rate of 35% primarily due to the effects of tax credits, state income taxes, utility rate-making, other permanent book-to-tax differences and income received following CPPL’s IPO that is not subject to income tax at the partnership level. The effective tax rate is impacted by CPPL’s IPO which modified the ownership structure and now reflects CPPL earnings for which the noncontrolling public limited partners are directly responsible for the related income taxes. CPG consolidates the pre-tax income related to the noncontrolling public limited partners’ share of partnership earnings but excludes the related tax provision. The effective tax rate for 2014 differs from the Federal tax rate of 35% primarily due to the effects of tax credits, state income taxes, utility rate-making, and other permanent book-to-tax differences.

Pension and Other Postretiremen

Pension and Other Postretirement Benefits	9 Months Ended
	Sep. 30, 2015
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 its employees. 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. The majority of employees may become eligible for these benefits if they reach retirement age while working for CPG. The expected cost of such benefits is accrued during the employees’ years of service. Current rates charged to customers of CPG include postretirement benefit costs. Cash contributions are remitted to grantor trusts. Prior to the Separation, CPG was a participant in the consolidated NiSource defined benefit retirement plans and was allocated a ratable portion of NiSource’s grantor trusts for the plans in which its employees and retirees participated. As a result, CPG followed multiple employer accounting under the provisions of GAAP. CPG continues to follow multiple employer accounting following the Separation. As of July 1, 2015, in connection with the Separation, accrued pension and postretirement benefit obligations for CPG participants and related plan assets were transferred to CPG. This event required a remeasurement of benefit obligations in accordance with ASC 715, Compensation - Retirement Benefits . Certain of CPG's actuarial assumptions were updated in connection with the remeasurement. As of July 1, 2015, CPG selected discount rates of 4.04% and 4.26% for determining the pension and postretirement benefit obligations, respectively. For the postretirement plans, CPG assumed a health care cost trend rate of 8.73% for the remainder of 2015, trending to 4.50% by 2022 . CPG also selected an estimated long-term rate of return assumption of 8.10% for pension plan assets and 7.96% for postretirement plan assets. These assumptions were used in the determination of the net periodic benefit cost and obligation for the period from July 1, 2015 through December 31, 2015. For the nine months ended September 30, 2015 , CPG has made no contributions to its pension plans and contributed $3.0 million to its other postretirement benefit plans. The following table provides the components of CPG's net periodic benefits cost for the three and nine months ended September 30, 2015 and 2014 : Pension Benefits Other Postretirement Benefits Three Months Ended September 30, (in millions) 2015 2014 2015 2014 Components of Net Periodic Benefit Cost (Income) Service cost $ 1.6 $ 1.3 $ 0.2 $ 0.2 Interest cost 4.0 2.4 1.2 1.2 Expected return on assets (7.0 ) (4.2 ) (4.6 ) (4.0 ) Amortization of prior service (credit) cost (0.3 ) (0.2 ) (0.2 ) 0.1 Recognized actuarial loss (gain) 2.6 1.2 (0.1 ) — Total Net Periodic Benefit Cost (Income) $ 0.9 $ 0.5 $ (3.5 ) $ (2.5 ) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, (in millions) 2015 2014 2015 2014 Components of Net Periodic Benefit Cost (Income) Service cost $ 4.3 $ 3.7 $ 0.8 $ 0.8 Interest cost 11.0 10.3 3.5 3.5 Expected return on assets (21.0 ) (17.9 ) (13.8 ) (12.3 ) Amortization of prior service (credit) cost (0.9 ) (0.7 ) (0.5 ) 0.1 Recognized actuarial loss (gain) 7.3 4.9 (0.1 ) — Total Net Periodic Benefit Cost (Income) $ 0.7 $ 0.3 $ (10.1 ) $ (7.9 )

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Fair Value	Fair Value CPG 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. CPG's long-term debt and long-term debt-affiliated are 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 and 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. These fair value measurements are classified as Level 2 within the fair value hierarchy. For the nine months ended September 30, 2015 and for the year ended December 31, 2014 , 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 September 30, 2015 Estimated Fair Value as of September 30, 2015 Carrying Amount as of Dec. 31, 2014 Estimated Fair Value as of Dec. 31, 2014 Current portion of long-term debt-affiliated $ — $ — $ 115.9 $ 120.0 Long-term debt 2,746.0 2,682.3 — — Long-term debt-affiliated — — 1,472.8 1,550.4

Share-Based Compensation

Share-Based Compensation	9 Months Ended
	Sep. 30, 2015
Share-based Compensation [Abstract]
Share-Based Compensation	Share-Based Compensation Prior to the Separation, CPG employees participated in NiSource's Omnibus Incentive Plan (the "NiSource Plan") and had outstanding awards under the NiSource Director Stock Incentive Plan (“NiSource Director Plan”), which was terminated in 2010. Upon the Separation, outstanding CPG employee restricted stock units, performance units and employee director awards previously issued under the NiSource Plan and NiSource Director Plan were adjusted and converted into new CPG share-based awards under the Columbia Pipeline Group, Inc. 2015 Omnibus Incentive Plan (the "Omnibus Plan") using a formula designed to preserve the intrinsic value and fair value of the awards immediately prior to the Separation. The performance targets applicable to the performance units were frozen at the levels achieved as of the Separation and pro-rated to reflect the proportion of the service period completed. Under the Omnibus Plan, these awards represent restricted stock units with no performance contingencies. All adjusted awards retained the vesting schedule of the original awards. The Omnibus Plan term began on the effective date of the Separation. The Omnibus Plan provides for awards to employees and non-employee directors of incentive and nonqualified stock options, stock appreciation rights, restricted stock and restricted stock units, performance shares, performance units, cash-based awards and other stock-based awards. The Omnibus Plan provides that the number of shares of common stock of CPG available for awards is 8,000,000 . At September 30, 2015 , there were 7,673,737 shares reserved for future awards under the Omnibus Plan. CPG recognized stock-based employee compensation expense of $0.1 million and $2.0 million during the three months ended September 30, 2015 and 2014 , respectively, and $3.2 million and $3.2 million during the nine months ended September 30, 2015 and 2014 , respectively. CPG recognized related tax benefits of zero and $0.7 million during the three months ended September 30, 2015 and 2014 , respectively, and $1.2 million and $1.2 million during the nine months ended September 30, 2015 and 2014 , respectively. As of September 30, 2015 , the total remaining unrecognized compensation cost related to nonvested awards amounted to $37.7 million , which will be amortized over the weighted-average remaining requisite service period of 1.8 years. Restricted Stock Units and Restricted Stock . In 2015 , CPG granted restricted stock units and shares of restricted stock of 129,104 , subject to service conditions. The total grant date fair value of the shares of restricted stock units and shares of restricted stock was $3.6 million , based on the average market price of CPG’s common stock at the date of each grant less the present value of any dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. As of September 30, 2015, 128,939 nonvested (all of which are expected to vest) restricted stock units and shares of restricted stock were granted and outstanding for the 2015 award. In 2015 , NiSource granted restricted stock units and shares of restricted stock that were converted into 450,107 CPG restricted stock units at Separation, subject to service conditions. The total grant date fair value of the shares of restricted stock units and shares of restricted stock was $11.6 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of any dividends not received during the vesting period converted into CPG common stock awards, which will be expensed, net of forfeitures, over the vesting period which is generally three years. As of September 30, 2015 , 450,107 nonvested (all of which are expected to vest) restricted stock units and shares of restricted stock were granted and outstanding for the 2015 award. In 2014 , NiSource granted restricted stock units and shares of restricted stock that were converted into 198,532 CPG restricted stock units at Separation, subject to service conditions. The total grant date fair value of the restricted stock units and shares of restricted stock was $4.2 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period, which will be expensed, net of forfeitures, over the vesting period which is generally three years. As of September 30, 2015 , 198,532 nonvested (all of which are expected to vest) restricted stock units and shares of restricted stock were granted and outstanding for the 2014 award. In 2013 , NiSource granted restricted stock units and shares of restricted stock that were converted into 31,655 CPG restricted stock units at Separation, subject to service conditions. The total grant date fair value of the restricted stock units and shares of restricted stock was $0.5 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period converted into CPG common stock awards, which will be expensed, net of forfeitures, over the vesting period which is generally three years. As of September 30, 2015 , 30,087 nonvested (all of which are expected to vest) restricted stock units and shares of restricted stock were granted and outstanding for the 2013 award. If the employee terminates employment before the service conditions lapse under the 2013, 2014 and 2015 awards due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the service conditions will lapse on the date of such termination with respect to a pro rata portion of the restricted stock units and shares of restricted stock. In the event of a Change-in-Control (as defined in the award agreement), all unvested shares of restricted stock and restricted stock units awarded prior to 2015 will immediately vest and all unvested shares of restricted stock and restricted stock units awarded in 2015 will immediately vest upon termination of employment occurring in connection with a change-in-control. Termination due to any other reason will result in all unvested shares of restricted stock and restricted stock units awarded being forfeited effective on the employee's date of termination. Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested at December 31, 2014 230,187 $ 20.27 Performance shares converted to restricted shares at Separation 1,460,401 15.66 Granted 579,211 26.30 Forfeited (165 ) 28.25 Vested (1,568 ) 18.24 Nonvested and Expected to Vest at September 30, 2015 2,268,066 $ 18.85 Performance Shares . In 2015 , CPG granted 161,504 performance shares subject to performance and service conditions. The grant date fair-value of the awards was $4.5 million , based on the average market price of CPG’s common stock at the date of grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. The performance condition is based on achievement of relative total shareholder return, a non-GAAP market measure that CPG defines as the annualized growth in the dividends and share price of a share of CPG’s common stock (calculated using a 20 trading day average of CPG’s closing price, over a period beginning July 31, 2015 and ending on June 30, 2018) compared to the total shareholder return performance of a predetermined peer group of companies. The service conditions lapse on July 12, 2018 when the shares vest provided the performance criteria are satisfied. As of September 30, 2015 , 161,504 nonvested performance shares were granted and outstanding of the 2015 award. In 2014 , NiSource granted performance shares that were converted to 586,219 CPG restricted stock units at Separation, subject to performance and service conditions. The grant date fair-value of the awards was $11.3 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. Through the conversion, the performance contingencies were removed from these awards. The service conditions lapse on February 28, 2017 when the shares vest. As of September 30, 2015 , 586,219 nonvested restricted stock units were granted and outstanding of the 2014 award. In 2013 , NiSource granted performance shares that were converted to 874,182 CPG restricted stock units at Separation, subject to performance and service conditions. The grant date fair-value of the awards was $11.6 million , based on the average market price of NiSource’s common stock at the date of each grant less the present value of dividends not received during the vesting period which will be expensed, net of forfeitures, over the three year requisite service period. Through the conversion, the performance contingencies were removed from these awards. The service conditions lapse on January 30, 2016 when the shares vest. As of September 30, 2015 , 874,182 nonvested restricted stock units were granted and outstanding for the 2013 award. If the employee terminates employment before the performance and service conditions lapse under the 2013, 2014 and 2015 awards due to (1) Retirement or Disability (as defined in the award agreement), or (2) death, the employment conditions will lapse with respect to a pro rata portion of the performance shares payable at target on the date of termination provided the performance criteria are met. In the event of a Change-in-Control (as defined in the award agreement), all unvested performance shares will immediately vest. Termination due to any other reason will result in all performance shares awarded being forfeited effective on the employee’s date of termination. Contingent Awards Weighted Average Grant Date Fair Value Nonvested at December 31, 2014 1,460,401 $ 15.66 Performance shares converted to restricted shares at Separation (1,460,401 ) 15.66 Granted 161,504 28.16 Forfeited — — Vested — — Nonvested and Expected to Vest at September 30, 2015 161,504 $ 28.16 Non-employee Director Awards . Currently, restricted stock units are granted annually to non-employee directors, subject to a non-employee director’s election to defer receipt of such restricted stock unit award. The non-employee director’s restricted stock units vest on the first anniversary of the grant thereof subject to special pro-rata vesting rules in the event of Retirement or Disability (as defined in the award agreement), or death. The vested restricted stock units are payable as soon as practicable following vesting except as otherwise provided pursuant to the non-employee director’s election to defer. As of September 30, 2015 , a total of 51,696 units are outstanding to non-employee directors under the Omnibus Plan. Of these awards, 13,495 were granted under the NiSource Plan and converted into CPG awards while the remaining 38,201 were granted by CPG subsequent to the Separation. Fully vested restricted stock units that remained outstanding under the NiSource Plan and NiSource Director Plan as of the Separation date were converted into CPG awards. All such awards shall be distributed to the directors upon their separation from CPG's board of directors or such later date as elected. As of September 30, 2015 , 225,431 restricted stock units remain outstanding. 401(k) Match, Profit Sharing and Company Contribution. CPG has a voluntary 401(k) savings plan covering eligible employees that allows for periodic discretionary matches as a percentage of each participant’s contributions. CPG also has a retirement savings plan that provides for discretionary profit sharing contributions to eligible employees based on earnings results; and eligible exempt employees hired after January 1, 2010, receive a non-elective company contribution of three percent of eligible pay. CPG recognized 401(k) match, profit sharing and non-elective contribution expense of $2.2 million , and $2.3 million , respectively, for the three months ended September 30, 2015 and 2014 and $6.6 million , and $5.9 million , respectively, for the nine months ended September 30, 2015 and 2014 .

Other Commitments and Contingen

Other Commitments and Contingencies	9 Months Ended
	Sep. 30, 2015
Other Commitments and Contingencies [Abstract]
Other Commitments and Contingencies	Other Commitments and Contingencies A. Guarantees and Indemnities. In the normal course of its business, CPG and certain subsidiaries enter into various agreements providing financial or performance assurance to third parties on behalf of 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 a parent or subsidiary on a stand-alone basis, thereby facilitating the extension of sufficient credit to accomplish the parent or subsidiaries' intended commercial purposes. The total guarantees and indemnities in existence at September 30, 2015 and the years in which they expire were: (in millions) Total 2015 2016 2017 2018 2019 After Letters of credit $ 18.1 $ — $ 18.1 $ — $ — $ — $ — Other guarantees 43.0 — 0.6 2.0 — — 40.4 Total commercial commitments $ 61.1 $ — $ 18.7 $ 2.0 $ — $ — $ 40.4 Guarantees of Debt. Certain of CPG's subsidiaries, including OpCo GP, Columbia OpCo and CEG have guaranteed payment of $2,750.0 million in aggregated principal amount of CPG's senior notes. Each guarantor of CPG's obligations 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. CPG does not anticipate its subsidiaries will have any difficulty maintaining compliance. Lines and Letters of Credit. 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 this facility will be utilized as credit support for Columbia OpCo and its subsidiaries and the remaining $750.0 million of this 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. As of September 30, 2015 , CPG had $225.0 million in outstanding borrowings and $18.1 million in letters of credit outstanding under its revolving credit facility. CPPL 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 September 30, 2015 , CPPL had $20.0 million in outstanding borrowings and no letters of credit under its revolving credit facility. Other Guarantees or Obligations. CPG has on deposit a letter of credit with MUFG Union Bank, N.A., Collateral Agent, in a debt service reserve account in association with Millennium Pipeline's notes as required under the Deposit and Disbursement Agreement that governs the Millennium Pipeline notes. This account is to be drawn upon by the note holders in the event that Millennium Pipeline is delinquent on its principal and interest payments. The value of CPG’s letter of credit represents 47.5% (CPG’s ownership interest in Millennium Pipeline) of the debt service reserve account requirement, or $16.2 million . The total exposure for CPG is $16.2 million . CPG has an accrued liability of $1.5 million related to the inception date fair value of this guarantee as of September 30, 2015 . B. Other Legal Proceedings. In the normal course of its business, CPG has been named as a defendant in various legal proceedings. In the opinion of CPG, the ultimate disposition of these currently asserted claims will not have a material impact on CPG’s condensed consolidated financial statements. C. Environmental Matters. CPG’s operations are subject to environmental statutes and regulations related to air quality, water quality, hazardous waste and solid waste. CPG 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 CPG’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 CPG will not incur fines and penalties. As of September 30, 2015 and December 31, 2014 , CPG has liabilities recorded of approximately $8.5 million and $14.3 million , respectively, to cover environmental remediation at various sites. The current portion of these liabilities 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). CPG accrues for costs associated with environmental remediation obligations when the incurrence of such costs is probable and the amounts can be reasonably estimated. The original estimates for cleanup can differ materially from the amount ultimately expended. The actual future expenditures depend on many factors, including currently enacted laws and regulations, the nature and extent of contamination, the method of cleanup, and the availability of cost recovery from customers. As of the date of these financial statements, these expenditures are not estimable at some sites. CPG periodically adjusts its accrual as information is collected and estimates become more refined. Air The actions listed below could require further reductions in emissions from various emission sources. CPG 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, CPG 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 CPG combustion sources may need to be assessed and mitigated. CPG 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. CPG will continue to monitor this matter and cannot estimate the impact of these rules at this time. Waste CPG has liabilities associated with the cleanup of some of its former operations. Four sites are associated with its former propane operations and ten sites associated with former petroleum operations. The total liability related to these sites was $6.5 million and $12.5 million at September 30, 2015 and December 31, 2014 , respectively. The liability represents CPG’s best estimate of the cost to remediate the facilities.

Accumulated Other Comprehensive

Accumulated Other Comprehensive Loss	9 Months Ended
	Sep. 30, 2015
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 and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of July 1, 2015 $ (13.9 ) $ (10.6 ) $ (24.5 ) Other comprehensive income before reclassifications (0.9 ) (1.4 ) (2.3 ) Amounts reclassified from accumulated other comprehensive income 0.2 1.3 1.5 Net current-period other comprehensive income (0.7 ) (0.1 ) (0.8 ) Balance as of September 30, 2015 $ (14.6 ) $ (10.7 ) $ (25.3 ) Nine Months Ended September 30, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2015 $ (16.6 ) $ (17.9 ) $ (34.5 ) Other comprehensive income before reclassifications (0.9 ) 5.8 4.9 Amounts reclassified from accumulated other comprehensive income 0.7 1.4 2.1 Net current-period other comprehensive income (0.2 ) 7.2 7.0 Allocation of accumulated other comprehensive loss to noncontrolling interest 2.2 — 2.2 Balance as of September 30, 2015 $ (14.6 ) $ (10.7 ) $ (25.3 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits. Three Months Ended September 30, 2014 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of July 1, 2014 $ (17.1 ) $ (8.4 ) $ (25.5 ) Other comprehensive income before reclassifications — (0.1 ) (0.1 ) Amounts reclassified from accumulated other comprehensive income 0.3 (0.1 ) 0.2 Net current-period other comprehensive income 0.3 (0.2 ) 0.1 Balance as of September 30, 2014 $ (16.8 ) $ (8.6 ) $ (25.4 ) Nine Months Ended September 30, 2014 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2014 $ (17.6 ) $ (8.2 ) $ (25.8 ) Other comprehensive income before reclassifications — (0.1 ) (0.1 ) Amounts reclassified from accumulated other comprehensive income 0.8 (0.3 ) 0.5 Net current-period other comprehensive income 0.8 (0.4 ) 0.4 Balance as of September 30, 2014 $ (16.8 ) $ (8.6 ) $ (25.4 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits. Equity Investment Millennium Pipeline is an equity method investment, and, therefore, CPG is required to recognize a proportional share of Millennium Pipeline’s OCI. The remaining unrecognized loss at September 30, 2015 of $14.6 million , after tax, related to terminated interest rate swaps is being amortized over the 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 $14.6 million , after tax, and $16.6 million , after tax, at September 30, 2015 and December 31, 2014 , respectively, is included in gains and losses on cash flow hedges above.

Other, Net

Other, Net	9 Months Ended
	Sep. 30, 2015
Other Income and Expenses [Abstract]
Other, Net	Other, Net Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 AFUDC Equity $ 6.5 $ 3.9 $ 15.0 $ 8.2 Miscellaneous 0.2 (0.3 ) 1.6 — Total Other, net $ 6.7 $ 3.6 $ 16.6 $ 8.2

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	9 Months Ended
	Sep. 30, 2015
Supplemental Cash Flow Information [Abstract]
Supplemental Cash Flow Information	Supplemental Cash Flow Information The following table provides additional information regarding CPG’s Condensed Statements of Consolidated Cash Flows (unaudited) for the nine months ended September 30, 2015 and 2014 : (in millions) 2015 2014 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities (1) $ 219.9 $ 96.4 Schedule of interest and income taxes paid: Cash paid for interest, net of interest capitalized amounts $ 41.9 $ 55.0 Cash paid for income taxes (2) 30.8 46.9 (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). (2) Cash paid for income taxes for the nine months ended September 30, 2015 includes $20.9 million paid to NiSource under the Tax Allocation Agreement.

Concentration of Credit Risk

Concentration of Credit Risk	9 Months Ended
	Sep. 30, 2015
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 and nine months ended September 30, 2015 and 2014 . The following tables provide this customer's operating revenues and percentage of total operating revenues for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, 2015 2014 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 35.3 11.0 % $ 36.2 11.4 % Nine Months Ended September 30, 2015 2014 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 120.4 12.3 % $ 119.8 11.9 % (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 we receive 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 CPG.

CPPL Initial Public Offering (T

CPPL Initial Public Offering (Tables)	9 Months Ended
	Sep. 30, 2015
Equity [Abstract]
Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest	Three Months Ended Nine Months Ended (in millions) 2015 2015 Net income attributable to CPG $ 63.0 $ 203.8 Increase in CPG’s net parent investment for the sale of 8.4% of Columbia OpCo — 227.1 Change from net income attributable to CPG and transfers to noncontrolling interest $ 63.0 $ 430.9

Earnings Per Share (Tables)

Earnings Per Share (Tables)	9 Months Ended
	Sep. 30, 2015
Earnings Per Share [Abstract]
Schedule of Earnings Per Share, Basic and Diluted [Table Text Block]	Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 Basic average common shares outstanding 317.6 317.6 317.6 317.6 Dilutive potential common shares: Shares restricted under stock plans 0.8 — 0.8 — Diluted average common shares 318.4 317.6 318.4 317.6

Transactions with Affiliates (T

Transactions with Affiliates (Tables)	9 Months Ended
	Sep. 30, 2015
Related Party Transactions [Abstract]
Schedule of Transactions with Affiliates	Statement of Operations. Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 Transportation revenues $ — $ 18.8 $ 47.5 $ 66.2 Storage revenues — 13.2 26.2 40.1 Other revenues — 0.1 0.2 0.3 Operation and maintenance expense — 32.1 52.9 89.9 Interest expense — 14.4 29.3 39.1 Interest income — 0.2 2.5 0.5 Balance Sheet. (in millions) September 30, 2015 December 31, 2014 Accounts receivable $ — $ 180.0 Current portion of long-term debt — 115.9 Short-term borrowings — 252.5 Accounts payable — 53.6 Long-term debt — 1,472.8
Schedule of Related Party Transactions, Long-Term Debt	Origination Date Interest Rate Maturity Date September 30, 2015 December 31, 2014 (in millions) November 28, 2005 (1) 5.41 % November 30, 2015 $ — $ 115.9 November 28, 2005 5.45 % November 28, 2016 — 45.3 November 28, 2005 5.92 % November 28, 2025 — 133.5 November 28, 2012 4.63 % November 28, 2032 — 45.0 November 28, 2012 4.94 % November 30, 2037 — 95.0 December 19, 2012 5.16 % December 21, 2037 — 55.0 November 28, 2012 5.26 % November 28, 2042 — 170.0 December 19, 2012 5.49 % December 18, 2042 — 95.0 December 9, 2013 (2) 4.75 % December 31, 2016 — 834.0 Total Long-term Debt $ — $ 1,588.7

Asset Retirement Obligations (T

Asset Retirement Obligations (Tables)	9 Months Ended
	Sep. 30, 2015
Asset Retirement Obligation [Abstract]
Changes In Company's Liability for Asset Retirement Obligations	(in millions) 2015 2014 Balance as of January 1, $ 23.2 $ 26.3 Accretion expense 0.9 1.1 Additions 0.4 2.0 Settlements — — Change in estimated cash flows (1.6 ) (0.2 ) Balance as of September 30, $ 22.9 $ 29.2

Pension and Other Postretirem35

Pension and Other Postretirement Benefits (Tables)	9 Months Ended
	Sep. 30, 2015
Pension and Other Postretirement Benefit Expense [Abstract]
Components Of The Plans' Net Periodic Benefits Cost	Pension Benefits Other Postretirement Benefits Three Months Ended September 30, (in millions) 2015 2014 2015 2014 Components of Net Periodic Benefit Cost (Income) Service cost $ 1.6 $ 1.3 $ 0.2 $ 0.2 Interest cost 4.0 2.4 1.2 1.2 Expected return on assets (7.0 ) (4.2 ) (4.6 ) (4.0 ) Amortization of prior service (credit) cost (0.3 ) (0.2 ) (0.2 ) 0.1 Recognized actuarial loss (gain) 2.6 1.2 (0.1 ) — Total Net Periodic Benefit Cost (Income) $ 0.9 $ 0.5 $ (3.5 ) $ (2.5 ) Pension Benefits Other Postretirement Benefits Nine Months Ended September 30, (in millions) 2015 2014 2015 2014 Components of Net Periodic Benefit Cost (Income) Service cost $ 4.3 $ 3.7 $ 0.8 $ 0.8 Interest cost 11.0 10.3 3.5 3.5 Expected return on assets (21.0 ) (17.9 ) (13.8 ) (12.3 ) Amortization of prior service (credit) cost (0.9 ) (0.7 ) (0.5 ) 0.1 Recognized actuarial loss (gain) 7.3 4.9 (0.1 ) — Total Net Periodic Benefit Cost (Income) $ 0.7 $ 0.3 $ (10.1 ) $ (7.9 )

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2015
Fair Value Disclosures [Abstract]
Carrying Amount And Estimated Fair Values Of Financial Instruments	(in millions) Carrying Amount as of September 30, 2015 Estimated Fair Value as of September 30, 2015 Carrying Amount as of Dec. 31, 2014 Estimated Fair Value as of Dec. 31, 2014 Current portion of long-term debt-affiliated $ — $ — $ 115.9 $ 120.0 Long-term debt 2,746.0 2,682.3 — — Long-term debt-affiliated — — 1,472.8 1,550.4

Share-Based Compensation (Table

Share-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2015
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Other Share-based Compensation, Activity	Restricted Stock Units Weighted Average Grant Date Fair Value Nonvested at December 31, 2014 230,187 $ 20.27 Performance shares converted to restricted shares at Separation 1,460,401 15.66 Granted 579,211 26.30 Forfeited (165 ) 28.25 Vested (1,568 ) 18.24 Nonvested and Expected to Vest at September 30, 2015 2,268,066 $ 18.85
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Schedule of Other Share-based Compensation, Activity	Contingent Awards Weighted Average Grant Date Fair Value Nonvested at December 31, 2014 1,460,401 $ 15.66 Performance shares converted to restricted shares at Separation (1,460,401 ) 15.66 Granted 161,504 28.16 Forfeited — — Vested — — Nonvested and Expected to Vest at September 30, 2015 161,504 $ 28.16

Other Commitments and Conting38

Other Commitments and Contingencies Other Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2015
Commitments and Contingencies Disclosure [Abstract]
Contractual Obligation, Fiscal Year Maturity Schedule	The total guarantees and indemnities in existence at September 30, 2015 and the years in which they expire were: (in millions) Total 2015 2016 2017 2018 2019 After Letters of credit $ 18.1 $ — $ 18.1 $ — $ — $ — $ — Other guarantees 43.0 — 0.6 2.0 — — 40.4 Total commercial commitments $ 61.1 $ — $ 18.7 $ 2.0 $ — $ — $ 40.4

Accumulated Other Comprehensi39

Accumulated Other Comprehensive Loss (Tables)	9 Months Ended
	Sep. 30, 2015
Other Comprehensive Income (Loss), Tax [Abstract]
Components Of Accumulated Other Comprehensive Loss	Three Months Ended September 30, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of July 1, 2015 $ (13.9 ) $ (10.6 ) $ (24.5 ) Other comprehensive income before reclassifications (0.9 ) (1.4 ) (2.3 ) Amounts reclassified from accumulated other comprehensive income 0.2 1.3 1.5 Net current-period other comprehensive income (0.7 ) (0.1 ) (0.8 ) Balance as of September 30, 2015 $ (14.6 ) $ (10.7 ) $ (25.3 ) Nine Months Ended September 30, 2015 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2015 $ (16.6 ) $ (17.9 ) $ (34.5 ) Other comprehensive income before reclassifications (0.9 ) 5.8 4.9 Amounts reclassified from accumulated other comprehensive income 0.7 1.4 2.1 Net current-period other comprehensive income (0.2 ) 7.2 7.0 Allocation of accumulated other comprehensive loss to noncontrolling interest 2.2 — 2.2 Balance as of September 30, 2015 $ (14.6 ) $ (10.7 ) $ (25.3 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits. Three Months Ended September 30, 2014 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated (1) Balance as of July 1, 2014 $ (17.1 ) $ (8.4 ) $ (25.5 ) Other comprehensive income before reclassifications — (0.1 ) (0.1 ) Amounts reclassified from accumulated other comprehensive income 0.3 (0.1 ) 0.2 Net current-period other comprehensive income 0.3 (0.2 ) 0.1 Balance as of September 30, 2014 $ (16.8 ) $ (8.6 ) $ (25.4 ) Nine Months Ended September 30, 2014 (in millions) Gains and Losses on Cash Flow Hedges (1) Pension and OPEB Items (1) Accumulated Other Comprehensive Loss (1) Balance as of January 1, 2014 $ (17.6 ) $ (8.2 ) $ (25.8 ) Other comprehensive income before reclassifications — (0.1 ) (0.1 ) Amounts reclassified from accumulated other comprehensive income 0.8 (0.3 ) 0.5 Net current-period other comprehensive income 0.8 (0.4 ) 0.4 Balance as of September 30, 2014 $ (16.8 ) $ (8.6 ) $ (25.4 ) (1) All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net (Tables)

Other, Net (Tables)	9 Months Ended
	Sep. 30, 2015
Other Income and Expenses [Abstract]
Schedule Of Other, Net	Three Months Ended Nine Months Ended (in millions) 2015 2014 2015 2014 AFUDC Equity $ 6.5 $ 3.9 $ 15.0 $ 8.2 Miscellaneous 0.2 (0.3 ) 1.6 — Total Other, net $ 6.7 $ 3.6 $ 16.6 $ 8.2

Supplemental Cash Flow Inform41

Supplemental Cash Flow Information (Tables)	9 Months Ended
	Sep. 30, 2015
Supplemental Cash Flow Information [Abstract]
Additional Information Regarding Condensed Statements of Consolidated and Combined Cash Flows	(in millions) 2015 2014 Supplemental Disclosures of Cash Flow Information Non-cash transactions: Capital expenditures included in current liabilities (1) $ 219.9 $ 96.4 Schedule of interest and income taxes paid: Cash paid for interest, net of interest capitalized amounts $ 41.9 $ 55.0 Cash paid for income taxes (2) 30.8 46.9 (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). (2) Cash paid for income taxes for the nine months ended September 30, 2015 includes $20.9 million paid to NiSource under the Tax Allocation Agreement.

Concentration of Credit Risk (T

Concentration of Credit Risk (Tables)	9 Months Ended
	Sep. 30, 2015
Risks and Uncertainties [Abstract]
Schedule of Concentration Of Credit Risk	The following tables provide this customer's operating revenues and percentage of total operating revenues for the three and nine months ended September 30, 2015 and 2014 : Three Months Ended September 30, 2015 2014 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 35.3 11.0 % $ 36.2 11.4 % Nine Months Ended September 30, 2015 2014 (in millions) Total Operating Revenues Percentage of Total Operating Revenues Total Operating Revenues Percentage of Total Operating Revenues Columbia Gas of Ohio (1) $ 120.4 12.3 % $ 119.8 11.9 % (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 we receive from Columbia Gas of Ohio in any given period.

Basis of Accounting Presentat43

Basis of Accounting Presentation (Details) shares in Millions, $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)mi	Sep. 30, 2014USD ($)	Jul. 01, 2015shares
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Pipeline Miles | mi	15,000
Common Stock, Shares, Issued | shares			317.6
Senior Notes	$ 2,722.3
Repayments of Related Party Debt	1,087.3
Distribution to NiSource	$ 1,450	$ 0

CPPL Initial Public Offering (N

CPPL Initial Public Offering (Narrative) (Details) - USD ($) $ in Millions	8 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Initial Public Offering [Line Items]
Issuance of common units of CPPL	$ 1,168.4	$ 1,168.4
Columbia Pipeline Partners LP [Member]
Initial Public Offering [Line Items]
Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest	53.50%
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
Noncontrolling Interest
Initial Public Offering [Line Items]
Issuance of common units of CPPL		$ 1,168.4
Common Units [Member]
Initial Public Offering [Line Items]
Partners' Capital Account, Units, Sold in Public Offering	53,833,107

CPPL Initial Public Offering (S

CPPL Initial Public Offering (Schedule of Change From Net Income Attributable to the Partnership and Transfers to Noncontrolling Interest) (Details) - USD ($) $ in Millions	3 Months Ended		8 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014
Initial Public Offering [Line Items]
Net income attributable to CPG	$ 63	$ 53.6	$ 203.8	$ 203.8	$ 205.5
Noncontrolling Interest, Increase from Subsidiary Equity Issuance				13.9
Change from net income attributable to the Partnership and transfers to noncontrolling interest	63		430.9
Noncontrolling Interest
Initial Public Offering [Line Items]
Noncontrolling Interest, Increase from Subsidiary Equity Issuance	$ 0		$ 227.1	$ 13.9

Earnings Per Share (Narrative)

Earnings Per Share (Narrative) (Details) - $ / shares shares in Millions	Aug. 20, 2015	Aug. 04, 2015	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Jul. 01, 2015
Earnings Per Share [Abstract]
Common Stock, Dividends, Per Share, Cash Paid	$ 0.125
Common Stock, Shares, Issued							317.6
Dividends Declared Per Common Share		$ 0.125	$ 0.25	$ 0	$ 0.25	$ 0
Dividends Payable, Date of Record		Oct. 30, 2015
Dividends Payable, Date to be Paid		Nov. 20, 2015

Earnings Per Share (Schedule of

Earnings Per Share (Schedule of Diluted Average Common Shares) (Details) - shares shares in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Basic Average Common Shares Outstanding	317.6	317.6	317.6	317.6
Shares restricted under stock plans	0.8	0	0.8	0
Diluted average common shares	318.4	317.6	318.4	317.6

Transactions with Affiliates (N

Transactions with Affiliates (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		8 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Dec. 05, 2014
Related Party Transaction [Line Items]
Interest Expense, Long-term Debt		$ 16.4		$ 31	$ 42.5
Allowance for Funds Used During Construction, Capitalized Interest		$ 2.8		$ 2.4	$ 6
Short-term Debt, Weighted Average Interest Rate	1.21%	0.68%	1.21%	1.21%	0.68%
Interest Expense, Short-term Borrowings	$ 0	$ 0.8		$ 0.7	$ 2.6
Accounts receivable-affiliated	0		$ 0	0		$ 180
Revolving credit facility, Maximum Borrowing Capacity	2,600		2,600	2,600
Short-term Debt	245		245	245		0
Default Provision Floor	50		50	50
Short-term borrowings-affiliated	0		0	0		252.5
Distribution to Parent				1,450	$ 0
Repayments of Related Party Debt				1,087.3
Transportation and Storage Services
Related Party Transaction [Line Items]
Accounts receivable-affiliated						34.5
Columbia OpCo
Related Party Transaction [Line Items]
Reimbursement of Preformation Capital			500
Money Pool
Related Party Transaction [Line Items]
Accounts receivable-affiliated						$ 145.5
Revolving credit facility, Maximum Borrowing Capacity	750		750	750
Revolving Credit Facility
Related Party Transaction [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	$ 1,500		$ 1,500	$ 1,500			$ 1,500
Notes Due 2016 [1]
Related Party Transaction [Line Items]
Debt Instrument, Maturity Date				Dec. 31, 2016
London Interbank Offered Rate (LIBOR)
Related Party Transaction [Line Items]
Basis Spread on Variable Rate				1.00%
London Interbank Offered Rate (LIBOR) | Notes Due 2016 [1]
Related Party Transaction [Line Items]
Basis Spread on Variable Rate				1.50%

Transactions with Affiliates (S

Transactions with Affiliates (Schedule of Affiliated Transactions) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Related Party Transaction [Line Items]
Transportation revenues	$ 0	$ 18.8	$ 47.5	$ 66.2
Storage revenues	0	13.2	26.2	40.1
Other revenues	0	0.1	0.2	0.3
Operation and maintenance	0	32.1	52.9	89.9
Interest expense	0	14.4	29.3	39.1
Interest income	0	$ 0.2	2.5	$ 0.5
Accounts receivable	0		0		$ 180
Current portion of long-term debt	0		0		115.9
Short-term borrowings	0		0		252.5
Accounts payable	0		0		53.6
Long-term debt-affiliated	$ 0		$ 0		$ 1,472.8

Transactions with Affiliates 50

Transactions with Affiliates (Schedule of Long-term Debt) (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Long-term Debt	$ 0	$ 1,588.7
Notes Due 2015
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2005
Debt Instrument, Interest Rate, Stated Percentage	5.41%
Debt Instrument, Maturity Date	Nov. 30, 2015
Long-term Debt	$ 0	115.9
Notes Due 2016
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2005
Debt Instrument, Interest Rate, Stated Percentage	5.45%
Debt Instrument, Maturity Date	Nov. 28, 2016
Long-term Debt	$ 0	45.3
Notes Due 2025
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2005
Debt Instrument, Interest Rate, Stated Percentage	5.92%
Debt Instrument, Maturity Date	Nov. 28, 2025
Long-term Debt	$ 0	133.5
Notes Due 2032
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2012
Debt Instrument, Interest Rate, Stated Percentage	4.63%
Debt Instrument, Maturity Date	Nov. 28, 2032
Long-term Debt	$ 0	45
Notes Due 2037
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2012
Debt Instrument, Interest Rate, Stated Percentage	4.94%
Debt Instrument, Maturity Date	Nov. 30, 2037
Long-term Debt	$ 0	95
Notes Due 2037 [1]
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Dec. 19, 2012
Debt Instrument, Interest Rate, Stated Percentage	5.16%
Debt Instrument, Maturity Date	Dec. 21, 2037
Long-term Debt	$ 0	55
Notes Due 2042
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Nov. 28, 2012
Debt Instrument, Interest Rate, Stated Percentage	5.26%
Debt Instrument, Maturity Date	Nov. 28, 2042
Long-term Debt	$ 0	170
Notes Due 2042 [1]
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Dec. 19, 2012
Debt Instrument, Interest Rate, Stated Percentage	5.49%
Debt Instrument, Maturity Date	Dec. 18, 2042
Long-term Debt	$ 0	95
Notes Due 2016 [1]
Schedule of Related Party Transactions, Long-Term Debt [Line Items]
Debt Instrument, Issuance Date	Dec. 9, 2013
Debt Instrument, Interest Rate, Stated Percentage	4.75%
Debt Instrument, Maturity Date	Dec. 31, 2016
Long-term Debt	$ 0	$ 834

Short-Term Borrowings (Narrativ

Short-Term Borrowings (Narrative) (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)$ / shares	Dec. 05, 2014USD ($)
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	$ 2,600
Funds Used to Support Columbia OpCo		$ 750
Funds to Support General Purposes		750
Default Provision Floor	50
Commercial Paper
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	1,000
CPPL
Short-term Debt [Line Items]
Default Provision Floor	$ 50
Minimum
Short-term Debt [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.125%
Distribution Policy, Minimum | $ / shares	$ 0.1675
Maximum
Short-term Debt [Line Items]
Line of Credit Facility, Commitment Fee Percentage	0.35%
Ratio of Indebtedness to Net Capital	1
Line of Credit
Short-term Debt [Line Items]
Line of Credit	$ 225
Line of Credit | CPPL
Short-term Debt [Line Items]
Line of Credit	20
Revolving Credit Facility
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	1,500	1,500
Letters of Credit Outstanding	18.1
Revolving Credit Facility | CPPL
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	500	$ 500
Letters of Credit Outstanding	0
Letter of Credit
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	250
Letter of Credit | CPPL
Short-term Debt [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	$ 50
Period 1 | Minimum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5.75
Period 1 | Maximum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Period 2 | Minimum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5.50
Period 2 | Maximum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Period 3 | Minimum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5
Acquisition Period | Minimum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	5.50
Acquisition Period | Maximum
Short-term Debt [Line Items]
Ratio of Indebtedness to Net Capital	1
Federal Funds Effective Swap Rate
Short-term Debt [Line Items]
Basis Spread on Variable Rate	0.50%
Federal Funds Effective Swap Rate | Minimum
Short-term Debt [Line Items]
Margin Rate	0.00%
Federal Funds Effective Swap Rate | Maximum
Short-term Debt [Line Items]
Margin Rate	0.65%
London Interbank Offered Rate (LIBOR)
Short-term Debt [Line Items]
Basis Spread on Variable Rate	1.00%
London Interbank Offered Rate (LIBOR) | Minimum
Short-term Debt [Line Items]
Margin Rate	0.00%
London Interbank Offered Rate (LIBOR) | Maximum
Short-term Debt [Line Items]
Margin Rate	0.65%
Eurodollar
Short-term Debt [Line Items]
Margin Rate	1.00%
Eurodollar | Minimum
Short-term Debt [Line Items]
Margin Rate	1.00%
Eurodollar | Maximum
Short-term Debt [Line Items]
Margin Rate	1.65%

Long-Term Debt (Narrative) (Det

Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	May. 22, 2015	Sep. 30, 2015
Debt Instrument [Line Items]
Senior Notes		$ 2,722.3
Debt Covenant Interest Increase		0.50%
Notes Due 2025
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage		5.92%
Debt Instrument, Issuance Date		Nov. 28, 2005
Debt Instrument, Maturity Date		Nov. 28, 2025
Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount		$ 2,750
Debt Instrument, Issuance Date	May 22, 2015
Senior Notes | Notes Due 2018
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500
Debt Instrument, Interest Rate, Stated Percentage	2.45%
Debt Instrument, Maturity Date	Jun. 1, 2018
Senior Notes | Notes Due 2020
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 750
Debt Instrument, Interest Rate, Stated Percentage	3.30%
Debt Instrument, Maturity Date	Jun. 1, 2020
Senior Notes | Notes Due 2025
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 1,000
Debt Instrument, Interest Rate, Stated Percentage	4.50%
Debt Instrument, Maturity Date	Jun. 1, 2025
Senior Notes | Notes Due 2045
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500
Debt Instrument, Interest Rate, Stated Percentage	5.80%
Debt Instrument, Maturity Date	Jun. 1, 2045

Gain on Sale of Assets (Narrati

Gain on Sale of Assets (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Gain On Sale of Assets [Abstract]
Gain on Conveyances	$ 36	$ 3	$ 49.6	$ 20.8
Gain on Conveyances Cash Received	35.8
Deferred Gains On Conveyances	$ 10.7		$ 10.7		$ 19.6

Goodwill (Narrative) (Details)

Goodwill (Narrative) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Goodwill [Line Items]
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	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Asset Retirement Obligation [Abstract]
Beginning Balance	$ 23.2	$ 26.3
Accretion expense	0.9	1.1
Additions	0.4	2
Settlements	0	0
Change in estimated cash flows	(1.6)	(0.2)
Ending Balance	$ 22.9	$ 29.2

Regulatory Matters (Narrative)

Regulatory Matters (Narrative) (Details) - USD ($) $ in Millions	Jan. 01, 2015	Feb. 01, 2015
Regulatory Assets and Liabilities Disclosure [Abstract]
Expected Modernization Investment	$ 319
Modernization Program Recovery		$ 320

Equity Method Investments (Narr

Equity Method Investments (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Schedule of Equity Method Investments [Line Items]
Return of Capital			$ 15.1	$ 0
Millennium Pipeline
Schedule of Equity Method Investments [Line Items]
Contributions	$ 1.4	$ 0	1.4	2.6
Distributions	13.3	14.2	37.5	26.1
Hardy Storage
Schedule of Equity Method Investments [Line Items]
Contributions	0	0	0	0
Distributions	0	0.5	1	1.5
Pennant
Schedule of Equity Method Investments [Line Items]
Contributions	0	9	0	61.2
Distributions	2.9	$ 0	5.6	$ 0
Return of Capital	$ 0.2		$ 2.4
Equity Method Investment, Initial Ownership Percentage	5.00%		5.00%
Equity Method Investment, Ownership Percentage	47.50%		47.50%
Cash Received from Buy-In			$ 12.7
Gain on Buy-In			$ 2.9
Pennant | Previous
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	50.00%		50.00%
Pennant | Maximum
Schedule of Equity Method Investments [Line Items]
Equity Method Investment, Ownership Percentage	33.33%		33.33%

Income Taxes (Narrative) (Detai

Income Taxes (Narrative) (Details)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Income Taxes [Line Items]
Effective income tax rates	33.80%	35.80%	33.90%	36.90%
Corporate Income Tax Rate			35.00%

Pension and Other Postretirem59

Pension and Other Postretirement Benefits (Narrative) (Details) - USD ($) $ in Millions	Jul. 01, 2015	Sep. 30, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Health Care Cost Trend Rate Assumed for Next Fiscal Year	8.73%
Defined Benefit Plan, Ultimate Health Care Cost Trend Rate	4.50%
Defined Benefit Plan, Year that Rate Reaches Ultimate Trend Rate	2,022
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.04%
Employer contributions		$ 0
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	8.10%
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation, Discount Rate	4.26%
Employer contributions		$ 3
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets	7.96%

Pension and Other Postretirem60

Pension and Other Postretirement Benefits (Components Of The Plans' Net Periodic Benefits Cost) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Service Cost	$ 1.6	$ 1.3	$ 4.3	$ 3.7
Interest cost	4	2.4	11	10.3
Expected return on assets	(7)	(4.2)	(21)	(17.9)
Amortization of prior service (credit) cost	(0.3)	(0.2)	(0.9)	(0.7)
Recognized actuarial loss (gain)	2.6	1.2	7.3	4.9
Total Net Periodic Benefits Cost	0.9	0.5	0.7	0.3
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service Cost	0.2	0.2	0.8	0.8
Interest cost	1.2	1.2	3.5	3.5
Expected return on assets	(4.6)	(4)	(13.8)	(12.3)
Amortization of prior service (credit) cost	(0.2)	0.1	(0.5)	0.1
Recognized actuarial loss (gain)	(0.1)	0	(0.1)	0
Total Net Periodic Benefits Cost	$ (3.5)	$ (2.5)	$ (10.1)	$ (7.9)

Fair Value (Carrying Amount And

Fair Value (Carrying Amount And Estimated Fair Values Of Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Current portion of long-term debt-affiliated	$ 0	$ 115.9
Current Portion of Long Term Debt-affiliated, Fair Value	0	120
Long-term Debt, Carrying amount	2,746	0
Long-term Debt, Estimated Fair Value	2,682.3	0
Long-term Debt-affiliated, Carrying Amount	0	1,472.8
Long-term Debt-affiliated, Estimated Fair Value	$ 0	$ 1,550.4

Share-Based Compensation (Narra

Share-Based Compensation (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Shares Available for Grant	8,000,000		8,000,000
Number of Shares Authorized	7,673,737		7,673,737
Allocated Share-based Compensation Expense	$ 0.1	$ 2	$ 3.2	$ 3.2
Tax Benefit from Compensation Expense	0	0.7	1.2	1.2
Compensation Cost Not yet Recognized	37.7		$ 37.7
Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition			1 year 10 months
Defined Contribution Plan, Cost Recognized	$ 2.2	$ 2.3	$ 6.6	$ 5.9
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted			579,211	198,532	31,655
Vested, Fair Value				$ 4.2	$ 0.5
Nonvested	2,268,066		2,268,066			230,187
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted			161,504	586,219	874,182
Vested, Fair Value			$ 4.5	$ 11.3	$ 11.6
Nonvested	161,504		161,504			1,460,401
NiSource Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted			450,107
Vested, Fair Value			$ 11.6
CPG Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted			129,104
Vested, Fair Value			$ 3.6
2013 Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	30,087		30,087
2013 Award | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	874,182		874,182
2014 Award | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	198,532		198,532
2014 Award | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	586,219		586,219
2015 Award | Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	161,504		161,504
2015 Award | NiSource Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	450,107		450,107
2015 Award | CPG Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested	128,939		128,939
Omnibus Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued			51,696
Omnibus Plan | NiSource Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued			13,495
Omnibus Plan | CPG Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued			38,201
Director Plan | Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Issued			225,431

Share-Based Compensation (Sched

Share-Based Compensation (Schedule of Transactions Of Restricted Stock Units) (Details) - Restricted Stock - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested Beginning Balance	230,187
Performance shares converted to restricted shares	1,460,401
Granted	579,211	198,532	31,655
Forfeited	(165)
Vested	(1,568)
Nonvested Ending Balance	2,268,066
Nonvested, Weighted Average Grant Date Fair Value	$ 18.85			$ 20.27
Converted, Weighted Average Grant Date Fair Value	15.66
Granted, Weighted Average Grant Date Fair Value	26.30
Forfeited, Weighted Average Grant Date Fair Value	28.25
Vested, Weighted Average Grant Date Fair Value	$ 18.24

Share-Based Compensation (Sch64

Share-Based Compensation (Schedule of Transactions of Contingent Awards) (Details) - Performance Shares - $ / shares	9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2013	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Nonvested Beginning Balance	1,460,401
Performance shares converted to restricted shares	(1,460,401)
Granted	161,504	586,219	874,182
Forfeited	0
Vested	0
Nonvested Ending Balance	161,504
Nonvested, Weighted Average Grant Date Fair Value	$ 28.16			$ 15.66
Converted, Weighted Average Grant Date Fair Value	15.66
Granted, Weighted Average Grant Date Fair Value	28.16
Forfeited, Weighted Average Grant Date Fair Value	0
Vested, Weighted Average Grant Date Fair Value	$ 0

Other Commitments and Conting65

Other Commitments and Contingencies Other Commitments and Contingencies (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)	Dec. 31, 2014USD ($)	Dec. 05, 2014USD ($)
Other Commitments [Line Items]
Line of Credit Facility Used For Credit Support for Subsidiaries	$ 750
Line of Credit Facility Used For Corporate Purposes	750
Revolving credit facility, Maximum Borrowing Capacity	2,600
Guarantor Obligations, Maximum Exposure	61.1
Accrual for Environmental Loss Contingencies	8.5	$ 14.3
Liability for Estimated Remediation Costs	$ 6.5	$ 12.5
Ozone Level Maximum	70 ppb
Percentage Reduction in Methane Emissions	95.00%
Hours of Operation	26,000
Replacement Years	3 years
Revolving Credit Facility
Other Commitments [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	$ 1,500		$ 1,500
Letters of Credit Outstanding	18.1
Line of Credit
Other Commitments [Line Items]
Line of Credit	225
Letter of Credit
Other Commitments [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	250
CPPL | Revolving Credit Facility
Other Commitments [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	500		$ 500
Letters of Credit Outstanding	0
CPPL | Line of Credit
Other Commitments [Line Items]
Line of Credit	20
CPPL | Letter of Credit
Other Commitments [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	$ 50
Millennium Pipeline
Other Commitments [Line Items]
Percentage of Ownership Interest	47.50%
Guarantor Obligations, Maximum Exposure	$ 16.2
Guarantees, Fair Value	1.5
Senior Notes
Other Commitments [Line Items]
Debt Instrument, Face Amount	2,750
Commercial Paper
Other Commitments [Line Items]
Revolving credit facility, Maximum Borrowing Capacity	1,000
Letter of Credit
Other Commitments [Line Items]
Guarantor Obligations, Maximum Exposure	$ 18.1

Other Commitments and Conting66

Other Commitments and Contingencies (Existence and Expiration of Commercial Commitments) (Details) $ in Millions	Sep. 30, 2015USD ($)
Other Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure	$ 61.1
Guarantee Obligations Maximum Exposure Year One	0
Guarantee Obligations Maximum Exposure Year Two	18.7
Guarantee Obligations Maximum Exposure Year Three	2
Guarantee Obligations Maximum Exposure Year Four	0
Guarantee Obligations Maximum Exposure Year Five	0
Guarantee Obligations Maximum Exposure Thereafter	40.4
Letter of Credit
Other Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure	18.1
Guarantee Obligations Maximum Exposure Year One	0
Guarantee Obligations Maximum Exposure Year Two	18.1
Guarantee Obligations Maximum Exposure Year Three	0
Guarantee Obligations Maximum Exposure Year Four	0
Guarantee Obligations Maximum Exposure Year Five	0
Guarantee Obligations Maximum Exposure Thereafter	0
Guarantee Type, Other
Other Commitments and Contingencies [Line Items]
Guarantor Obligations, Maximum Exposure	43
Guarantee Obligations Maximum Exposure Year One	0
Guarantee Obligations Maximum Exposure Year Two	0.6
Guarantee Obligations Maximum Exposure Year Three	2
Guarantee Obligations Maximum Exposure Year Four	0
Guarantee Obligations Maximum Exposure Year Five	0
Guarantee Obligations Maximum Exposure Thereafter	$ 40.4

Accumulated Other Comprehensi67

Accumulated Other Comprehensive Loss (Narrative) (Details) - Millennium Pipeline - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Loss [Line Items]
Other Comprehensive Income Unrecognized Gain Loss On Derivatives Arising During Period Net Of Tax	$ 14.6	$ 16.6
Debt Instrument, Maturity Date	Jun. 1, 2025

(Components Of Accumulated Othe

(Components Of Accumulated Other Comprehensive Loss) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	$ (24.5)	$ (25.5)	$ (34.5)	$ (25.8)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]	(2.3)	(0.1)	4.9	(0.1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	1.5	0.2	2.1	0.5
Other Comprehensive Income (Loss), Net of Tax	[1]	(0.8)	0.1	7	0.4
Allocation of Accumulated Other Comprehensive Loss To Noncontrolling Interest				0
Ending Balance	[1]	(25.3)	(25.4)	(25.3)	(25.4)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	(13.9)	(17.1)	(16.6)	(17.6)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]	(0.9)	0	(0.9)	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	0.2	0.3	0.7	0.8
Other Comprehensive Income (Loss), Net of Tax	[1]	(0.7)	0.3	(0.2)	0.8
Allocation of Accumulated Other Comprehensive Loss To Noncontrolling Interest	[1]			2.2
Ending Balance	[1]	(14.6)	(16.8)	(14.6)	(16.8)
Accumulated Defined Benefit Plans Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	[1]	(10.6)	(8.4)	(17.9)	(8.2)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	[1]	(1.4)	(0.1)	5.8	(0.1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	1.3	(0.1)	1.4	(0.3)
Other Comprehensive Income (Loss), Net of Tax	[1]	(0.1)	(0.2)	7.2	(0.4)
Allocation of Accumulated Other Comprehensive Loss To Noncontrolling Interest	[1]			0
Ending Balance	[1]	$ (10.7)	$ (8.6)	(10.7)	$ (8.6)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income (Loss) [Line Items]
Other Comprehensive Income (Loss), Net of Tax				7
Allocation of Accumulated Other Comprehensive Loss To Noncontrolling Interest				$ 2.2
[1]	All amounts are net of tax. Amounts in parentheses indicate debits.

Other, Net (Schedule of Other,

Other, Net (Schedule of Other, Net) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Other Income and Expenses [Abstract]
AFUDC Equity	$ 6.5	$ 3.9	$ 15	$ 8.2
Miscellaneous	0.2	(0.3)	1.6	0
Total Other, net	$ 6.7	$ 3.6	$ 16.6	$ 8.2

Supplemental Cash Flow Inform70

Supplemental Cash Flow Information (Narrative) (Details) $ in Millions	9 Months Ended
	Sep. 30, 2015USD ($)
Supplemental Cash Flow Information [Abstract]
Cash Paid for Taxes Under Tax Allocation Agreement	$ 20.9

Supplemental Cash Flow Inform71

Supplemental Cash Flow Information (Schedule of Supplemental Cash Flow Information) (Details) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014
Supplemental Cash Flow [Line Items]
Capital expenditures included in current liabilities	[1]	$ 219.9	$ 96.4
Cash paid for interest, net of interest capitalized amounts		41.9	55
Cash paid for income taxes(2)	[2]	$ 30.8	$ 46.9
[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).
[2]	Cash paid for income taxes for the nine months ended September 30, 2015 includes $20.9 million paid to NiSource under the Tax Allocation Agreement.

Concentration of Credit Risk (N

Concentration of Credit Risk (Narrative) (Details)	9 Months Ended
	Sep. 30, 2015
Risks and Uncertainties [Abstract]
Concentration Risk, Benchmark Description	10% of total operating revenues

(Schedule of Concentration Of C

(Schedule of Concentration Of Credit Risk) (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Concentration Risk [Line Items]
Revenues		$ 320.9	$ 318	$ 977	$ 1,007.3
Credit Concentration Risk
Concentration Risk [Line Items]
Revenues	[1]	$ 35.3	$ 36.2	$ 120.4	$ 119.8
Concentration Risk, Percentage	[1]	11.00%	11.40%	12.30%	11.90%
[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 we receive from Columbia Gas of Ohio in any given period.