Other Commitments And Contingencies (Narrative) (Details) (USD $)	9 Months Ended											3 Months Ended
	Sep. 30, 2013	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 MGP Sites	Dec. 31, 2013 MGP Sites	Mar. 31, 2014 Columbia Transmission [Member]	Dec. 31, 2013 Columbia Transmission [Member]	Mar. 31, 2014 Millennium Pipeline Company, L.L.C [Member]	Mar. 31, 2014 Guarantees Of Subsidiaries Debt [Member]	Mar. 31, 2014 Letters Of Credit [Member]	Mar. 31, 2014 Other Guarantees [Member]	Mar. 31, 2014 Maximum [Member] NIPSCO [Member]	Mar. 31, 2014 Revolving Credit Facility [Member]	Mar. 31, 2014 Commercial Paper [Member]
Other Commitments And Contingencies [Line Items]
Remaining Payments for Capital Improvements												$ 240,000,000
Revolving credit facility, maximum	2,000,000,000												2,000,000,000	1,500,000,000
Line of Credit Facility, Expiration Date	Sep. 28, 2018
Line of Credit Facility, Amount Outstanding													0
Commercial paper		297,500,000	433,600,000											297,500,000
Accounts receivable securitization facility borrowings		515,000,000	265,100,000
Additional purchase and sales agreement guarantees		73,500,000
Percentage of interest in Millennium								47.50%
Guarantor Obligations, Maximum Exposure, Undiscounted		8,695,900,000						16,200,000	7,710,500,000	30,500,000	142,400,000
Fair value of guarantee obligations								1,500,000
Recorded reserves to cover environmental remediation at various sites		135,100,000	143,900,000
Number of waste disposal sites identified by program				67
Liability for Estimated Remediation Costs				123,200,000	129,500,000	6,400,000	8,700,000
Payments for Capital Improvements												860,000,000
Reasonably possible remediation costs variance from reserve				$ 25,000,000