Note 4 - Fair Value Measurements (Detail) - Derivative Assets and Liabilities (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Netting of Cash Collateral [Member] | Natural Gas Derivatives [Member]
Assets	$ 33	[1]	$ 32	[1]
Liabilities	36		115
Fair Value, Inputs, Level 1 [Member] | Natural Gas Derivatives [Member]
Assets	8	[1]	11	[1]
Liabilities	(45)		(145)
Fair Value, Inputs, Level 2 [Member] | Natural Gas Derivatives [Member]
Assets	96	[1]	229	[1]
Liabilities	(30)		(67)
Fair Value, Inputs, Level 2 [Member] | Interest Rate Derivatives [Member]
Assets	3	[1]	13	[1]
Liabilities	0		(13)
Natural Gas Derivatives [Member]
Assets	137	[1],[2],[3]	272	[1],[2],[3]
Liabilities	$ (39)	[2],[3]	$ (97)	[2],[3]

[1] $4 million of premium at December 31, 2012 and $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.