Other Commitments And Contingencies (Narrative) (Details) (USD $) In Millions, unless otherwise specified																0 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011	Aug. 20, 2010 National Emission Standard For Hazardous Air Pollutants [Member]	Sep. 30, 2012 MGP Sites	Dec. 31, 2011 MGP Sites	Apr. 05, 2012 NiSource Finance [Member]	Jun. 30, 2008 Whiting Clean Energy [Member]	Sep. 30, 2012 Millennium Pipeline Company, L.L.C [Member]	Sep. 30, 2012 Columbia Transmission [Member]	Dec. 31, 2011 Columbia Transmission [Member]	Sep. 30, 2012 Guarantees Of Subsidiaries Debt [Member]	Sep. 30, 2012 Guarantees Supporting Energy Commodity Transactions Of Subsidiaries [Member]	Sep. 30, 2012 Letters Of Credit [Member]	Sep. 30, 2012 Other Guarantees [Member]	Sep. 30, 2012 Maximum [Member] Northern Indiana [Member]	Sep. 30, 2012 Minimum [Member] Northern Indiana [Member]	Sep. 30, 2012 Letters Of Credit [Member]	Dec. 31, 2011 Letters Of Credit [Member]	Sep. 30, 2012 TerminationDateMay152017 [Member]
Other Commitments And Contingencies [Line Items]
Guarantees	$ 7,856.2								$ 16.2			$ 7,120.9	$ 109.2	$ 36.9	$ 363.9
Revolving credit facility, maximum																				1,500.0
Credit facilities borrowings	0	725.0																36.9	37.5
Commercial paper	55.0	402.7
Accounts receivable securitization facility borrowings	170.3	231.7
Sale of Whiting Clean Energy to BPAE								216.7
Portion of working capital								16.1
Total executed purchase and sales agreement guarantees								220
Additional purchase and sales agreement guarantees	30.0
Face amount of notes							250.0
Percentage of interest in Millennium	47.50%								47.50%
Fair value of guarantee obligations									1.5
Recorded reserves to cover environmental remediation at various sites	162.8		173.5
Payments for capital improvements																827	777
Minimum estimates cost of compliance				20
Maximum estimates cost of compliance				25
Original number of facilities AOC covered under conduct characterization and remediation activities, approximately										245
Number of liquid removal points AOC covered under conduct characterization and remediation activities										13,000
Number of mercury measurement stations AOC covered under conduct characterization and remediation activities										2,200
Number of storage well locations AOC covered under conduct characterization and remediation activities										3,700
Proposed penalty of NOV asserts violations of Pennsylvania Clean Streams law and Pennsylvania Solid Waste Management act										1
Increased liability for estimated remediation costs						71.1				3.5	25.6
Liability for estimated remediation costs					134.3	139.5				24.9	30.0
Reasonably possible remediation costs variance from reserve					$ 25
Remaining number of facilities AOC covered under conduct characterization and remediation activities, approximately										50