Transfers Of Financial Assets (Narrative) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended				6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011	Dec. 31, 2011	Jun. 30, 2012 Columbia Gas Of Ohio Receivables Corporation [Member]	Jun. 30, 2012 Nipsco Accounts Receivable Corporation [Member]	Jun. 30, 2012 Columbia Gas Of Pennsylvania Receivables Corporation [Member]	Jun. 30, 2012 Maximum [Member] Accounts Receivable Program [Member]	Oct. 21, 2011 Maximum [Member] Columbia Gas Of Ohio Receivables Corporation [Member]	Oct. 23, 2009 Maximum [Member] Columbia Gas Of Ohio Receivables Corporation [Member]	Oct. 23, 2009 Maximum [Member] Nipsco Accounts Receivable Corporation [Member]	Mar. 15, 2010 Maximum [Member] Columbia Gas Of Pennsylvania Receivables Corporation [Member]
Assets and Associated Liabilities of Transfers Accounted for as Secured Borrowings [Line Items]
Carrying amount of trade receivables transferred							$ 106.1	$ 10.0
Accounts receivable securitization facility borrowings	193.2		193.2		231.7				515.0
Trade receivables, seasonal program maximum						77.1				240.0	200.0	200.0	75.0
Net receivables transferred	193.2		193.2		231.7
Securitization transaction fees	0.9	0.8	2.0	2.3
Commercial paper	$ 134.4		$ 134.4		$ 402.7