Note 4 - Fair Value Measurements (Detail) - Derivative Assets and Liabilities (USD $) In Millions, unless otherwise specified	Jun. 30, 2012		Dec. 31, 2011		Jun. 30, 2011
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 1 [Member]
Derivative Assets	$ 9		$ 11	[1]	$ 1
Derivative Liabilities	(103)		(145)		(52)
Natural Gas Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Assets	148		229	[1]	99
Derivative Liabilities	(48)		(68)		(17)
Natural Gas Derivatives [Member] | Netting [Member]
Derivative Assets	52		32	[1]	37
Derivative Liabilities	85		115		40
Natural Gas Derivatives [Member]
Derivative Assets	209	[2],[3]	272	[1],[2],[3]	137	[2],[3]
Derivative Liabilities	(66)	[2],[3]	(98)	[2],[3]	(29)	[2],[3]
Interest Rate Derivatives [Member] | Fair Value, Inputs, Level 2 [Member]
Derivative Assets	17		13	[1]	3
Derivative Liabilities	$ 0		$ (13)		$ 0

[1] $3 million at December 31, 2011 associated with weather derivatives 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.