Note 4 - Fair Value Measurements (Details) - Derivative Assets and Liabilities - Natural Gas Derivatives [Member] - USD ($) $ in Millions		Jun. 30, 2015	Dec. 31, 2014	Jun. 30, 2014
Note 4 - Fair Value Measurements (Details) - Derivative Assets and Liabilities [Line Items]
Derivative Assets	[1],[2]	$ 195	$ 284	$ 111
Derivative Liabilities	[2]	(45)	(93)	(62)
Netting of cash collateral	[1]	64	52	46
Netting of cash collateral		53	81	36
Fair Value, Inputs, Level 1 [Member]
Note 4 - Fair Value Measurements (Details) - Derivative Assets and Liabilities [Line Items]
Derivative Assets	[1]	3	58	8
Derivative Liabilities		(53)	(80)	(38)
Fair Value, Inputs, Level 2 [Member]
Note 4 - Fair Value Measurements (Details) - Derivative Assets and Liabilities [Line Items]
Derivative Assets	[1]	128	174	57
Derivative Liabilities		$ (45)	$ (94)	$ (60)

[1] Balances of $2 million at June 30, 2015, $3 million at December 31, 2014 and $3 million at June 30, 2014, associated with certain weather derivatives have been excluded, as they are accounted for based on intrinsic value rather than fair value.

[2] There were no significant unobservable inputs (Level 3) or significant transfers between Level 1, Level 2 or Level 3 for any of the dates presented.