Note 4 - Fair Value Measurements (Detail) - Derivative Assets and Liabilities (USD $) In Millions, unless otherwise specified	Sep. 30, 2012		Dec. 31, 2011		Sep. 30, 2011
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative Assets	$ 11	[1]	$ 11	[1]	$ 8	[1]
Derivative Liabilities	(55)		(145)		(72)
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Assets	100	[1]	229	[1]	120	[1]
Derivative Liabilities	(33)		(68)		(39)
Natural Gas Derivatives [Member] | Netting [Member]
Derivative Assets	47	[1]	32	[1]	27	[1]
Derivative Liabilities	46		115		52
Natural Gas Derivatives [Member]
Derivative Assets	158	[1],[2],[3]	272	[1],[2],[3]	155	[1],[2],[3]
Derivative Liabilities	(42)	[2],[3]	(98)	[2],[3]	(59)	[2],[3]
Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Assets	0	[1]	13	[1]	13	[1]
Derivative Liabilities	$ 0		$ (13)		$ 0

[1] $1 million premium at September 30, 2012, $3 million at December 31, 2011 associated with weather derivatives and less than $1 million premium at September 30, 2011 have been excluded as they are accounted for based on intrinsic value.

[2] There were no material unobservable inputs (Level 3) for any of the periods presented.

[3] There were no material transfers between Level 1, Level 2, or Level 3 for any of the periods presented.