Goodwill (Summary Of Changes In Goodwill Assets) (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011
Goodwill [Line Items]
Cost, beginning balance	$ 3,635,358	$ 3,635,874
Total Net, beginning balance	1,195,069	1,195,585
Reclassifications and other activity	12,503	(75)
Cost, ending balance	3,647,861	3,635,799
Total Net, ending balance	1,207,572	1,195,510
Accumulated Impairment, beginning balance	(2,440,289)	(2,440,289)
Reclassifications and other activity, Accumulated Impairment	0	0
Accumulated Impairment, ending balance	(2,440,289)	(2,440,289)
Regulated Businesses [Member]
Goodwill [Line Items]
Cost, beginning balance	3,399,368	3,399,884
Reclassifications and other activity	12,503	(75)
Cost, ending balance	3,411,871	3,399,809
Accumulated Impairment, beginning balance	(2,332,670)	(2,332,670)
Reclassifications and other activity, Accumulated Impairment	0	0
Accumulated Impairment, ending balance	(2,332,670)	(2,332,670)
Market-Based Operations [Member]
Goodwill [Line Items]
Cost, beginning balance	235,990	235,990
Reclassifications and other activity	0	0
Cost, ending balance	235,990	235,990
Accumulated Impairment, beginning balance	(107,619)	(107,619)
Reclassifications and other activity, Accumulated Impairment	0	0
Accumulated Impairment, ending balance	$ (107,619)	$ (107,619)