Nature Of Operations And Summary Of Significant Accounting Policies (Computation Of Diluted Average Common Shares) (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Diluted Average Common Shares Computation [Line Items]
Nonqualified stock options	144		9		0
Shares contingently issuable under employee stock plans	557		1,017		910
Shares restricted under stock plans	544		339		697
Forward Agreements	7,229	[1]	6,684	[1]	684	[1]

[1] On September 10, 2012, NiSource settled the Forward Agreements. Amounts included in diluted average common shares for the year ended December 31, 2012 are weighted for the period prior to settlement.