Note 4 - Fair Value Measurements (Detail) - Derivative Assets and Liabilities (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011
Natural gas derivatives
Derivative Assets	$ 257	[1],[2]	$ 272	[1],[2],[3]	$ 140	[1],[2],[3]
Derivative Liabilities	(93)	[1],[2]	(98)	[1],[2]	(28)	[1],[2]
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Natural gas derivatives
Derivative Assets	203		229	[3]	101	[3]
Derivative Liabilities	(68)		(68)		(15)
Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Natural gas derivatives
Derivative Assets	9		13	[3]	0	[3]
Derivative Liabilities	(10)		(13)		0
Fair Value, Inputs, Level 1 [Member]
Natural gas derivatives
Derivative Assets	7		11	[3]	1	[3]
Derivative Liabilities	(187)		(145)		(63)
Netting [Member]
Natural gas derivatives
Derivative Assets	47		32	[3]	38	[3]
Derivative Liabilities	$ 162		$ 115		$ 50

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

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

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