Equity Method Investments (Details) (USD $)	12 Months Ended			1 Months Ended	12 Months Ended			18 Months Ended		0 Months Ended	12 Months Ended				12 Months Ended
	Oct. 31, 2013	Oct. 31, 2012	Oct. 31, 2011	Jun. 30, 2012 Cardinal Pipeline Company [Member]	Oct. 31, 2013 Cardinal Pipeline Company [Member]	Oct. 31, 2012 Cardinal Pipeline Company [Member]	Oct. 31, 2011 Cardinal Pipeline Company [Member]	Jun. 30, 2012 Cardinal Pipeline Company [Member]	Jun. 22, 2012 Cardinal Pipeline Company [Member]	Jul. 01, 2013 Pine Needle Company [Member]	Oct. 31, 2013 Pine Needle Company [Member]	Oct. 31, 2012 Pine Needle Company [Member]	Oct. 31, 2011 Pine Needle Company [Member]	Jun. 30, 2013 Pine Needle Company [Member]	Oct. 31, 2013 South Star Energy Services [Member]	Oct. 31, 2012 South Star Energy Services [Member]	Oct. 31, 2011 South Star Energy Services [Member]	Oct. 31, 2013 Hardy Storage [Member]	Oct. 31, 2012 Hardy Storage [Member]	Oct. 31, 2011 Hardy Storage [Member]	Oct. 31, 2013 Constitution Pipeline Company [Member]
Schedule Of Equity Method Investments [Line Items]
Retained Earnings, Undistributed Earnings from Equity Method Investees	$ 0
Equity Method Investment Ownership Percentage					21.49%						45.00%			40.00%	15.00%			50.00%			24.00%
Equity Method Investment Additional Information											In June 2013, we entered into an agreement with Hess Corporation (Hess) to acquire their 5% membership interest in Pine Needle. Effective July 1, 2013, we acquired Hess’ 5% membership interest for $2.9 million. With the purchase of this additional 5% membership interest, our membership interest in Pine Needle increased from 40% to 45%.				In September 2013, GNGC contributed its retail natural gas marketing assets and customer accounts located in Illinois. AGL acquired these retail assets and customers from Nicor Inc. in December 2011 and additional retail natural gas assets and customer accounts in a separate transaction in June 2013. We made an additional $22.5 million capital contribution to SouthStar, maintaining our 15% equity ownership, related to this transaction.
Related Party Transaction Expenses From Transactions With Related Party					8,775,000	6,613,000	4,104,000				11,098,000	10,410,000	10,677,000					9,702,000	9,702,000	9,702,000
Due To Related Parties Current					755,000	855,000					940,000	914,000						808,000	808,000
Due From Related Parties Current															441,000	473,000
Summarized Financial Information Percentage					100.00%	100.00%	100.00%				100.00%	100.00%	100.00%		100.00%	100.00%	100.00%	100.00%	100.00%	100.00%	100.00%
Revenue From Related Parties															3,291,000	2,442,000	4,961,000
Contributions to and purchase of additional interest in equity method investments	41,348,000	3,566,000	6,222,000					9,800,000		2,900,000					22,500,000						15,900,000
Distributions of capital from equity method investments	4,700,000	5,372,000	3,029,000	5,400,000
Cardinal Permanent Financing									45,000,000
Equity Method Investment Description Of Principal Activities					Cardinal owns and operates an intrastate natural gas pipeline in North Carolina and is regulated by the NCUC. Cardinal has firm, long-term service agreements with local distribution companies for 100% of the firm transportation capacity on the pipeline, of which Piedmont subscribes to approximately 53%. Cardinal is dependent on the Williams – Transco pipeline system to deliver gas into its system for service to its customers.						Pine Needle LNG Company, L.L.C. (Pine Needle), a North Carolina limited liability company, owns an interstate LNG storage facility in North Carolina and is regulated by the FERC. Pine Needle has firm, long-term service agreements for 100% of the storage capacity of the facility, of which Piedmont subscribes to approximately 64%.				SouthStar primarily sells natural gas to residential, commercial and industrial customers in the southeastern United States, including Illinois, Ohio, New York, Maryland, North Carolina, South Carolina and Tennessee, with most of its business being conducted in the unregulated retail gas market in Georgia. We account for our investment in SouthStar using the equity method, as we have board representation with equal voting rights on significant governance matters and policy decisions, and thus, exercise significant influence over the operations of SouthStar.			Hardy Storage owns and operates an underground interstate natural gas storage facility located in Hardy and Hampshire Counties, West Virginia, that is regulated by the FERC. Hardy Storage has firm, long-term service agreements for 100% of the storage capacity of the facility, of which Piedmont subscribes to approximately 40%.			The purpose of the joint venture is to construct and operate approximately 120 miles of interstate natural gas pipeline and related facilities connecting shale natural gas supplies and gathering systems in Susquehanna County, Pennsylvania, to the Iroquois Gas Transmission and Tennessee Gas Pipeline systems in New York. We have committed to fund an amount in proportion to our ownership interest for the development and construction of the new pipeline, which is expected to cost approximately $680 million. we expect our total contributions will be an estimated $55 million and $92.1 million in our fiscal 2014 and 2015 years, respectively. The target in-service date of the project is March 2015. The capacity of the pipeline is 100% subscribed under fifteen year service agreements with two Marcellus producer-shippers with a negotiated rate structure.
Equity Method Investment Summarized Financial Information [Abstract]
Current Assets					15,179,000	9,179,000					9,225,000	11,937,000			194,793,000	152,422,000		7,641,000	10,302,000		10,944,000
Non Current Assets					116,414,000	120,437,000					74,710,000	77,463,000			136,753,000	9,803,000		161,282,000	164,374,000		62,438,000
Current Liabilities					2,637,000	1,786,000					3,531,000	4,278,000			76,304,000	42,197,000		12,378,000	14,534,000		7,960,000
Non Current Liabilities					45,273,000	45,702,000					35,391,000	35,851,000			53,000	1,000		87,184,000	95,061,000		0
Revenues					17,649,000	16,165,000	13,633,000				16,810,000	16,390,000	17,666,000		639,426,000	585,291,000	733,987,000	24,375,000	24,359,000	24,378,000	0
Gross Profit (Loss)					17,649,000	16,165,000	13,633,000				16,810,000	16,390,000	17,666,000		174,993,000	161,122,000	176,010,000	24,375,000	24,359,000	24,378,000	0
Income Before Income Taxes					9,361,000	10,433,000	6,473,000				5,804,000	5,832,000	5,763,000		103,146,000	94,631,000	103,704,000	10,582,000	9,939,000	9,657,000	3,459,000
Pipeline Subscription Capacity Percentage					100.00%																100.00%
Pipeline Transportation Capacity Subscribed					53.00%
Storage Capacity Subscription Percentage											100.00%							100.00%
Storage Capacity Subscribed											64.00%							40.00%
Additional Equity Method Ownership Percentage Acquired										5.00%
Estimated Piedmont Contributions To Pipeline Project Next Fiscal Year																					55,000,000
Estimated Piedmont Contributions To Pipeline Project In Two Fiscal Years																					92,100,000
Term Pipeline Subscription Agreements																					15 years
Estimated Pipeline Development And Construction Costs																					$ 680,000,000
Pipeline Target In Service Date																					March 2015