Risk Management And Hedging Activities (Schedule Of Cash Flow Hedges Included In Accumulated Other Comprehensive Income (Loss)) (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Derivative [Line Items]
Total AOCI	$ (15.5)	$ (21.2)	[1]
Commodity Derivatives [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Net deferred losses in AOCI	(5.4)	(1.8)
Interest Rate Contract [Member] | Cash Flow Hedging [Member]
Derivative [Line Items]
Net deferred losses in AOCI	$ (10.1)	$ (19.4)

[1] The financial information as of December 31, 2011 includes the results of Southeast Texas, a transfer of net assets between entities under common control that was accounted for as if the transfer occurred at the beginning of the period, and prior years are retrospectively adjusted to furnish comparative information similar to the pooling method.