Note 4 - Fair Value Measurements (Details) - Derivative Assets and Liabilities (USD $) In Millions, unless otherwise specified	Mar. 31, 2014		Dec. 31, 2013		Mar. 31, 2013
Fair Value, Inputs, Level 1 [Member] | Natural Gas Derivatives [Member]
Natural gas derivatives
Derivative Assets	$ 18	[1]	$ 6	[1]	$ 14	[1]
Derivative Liabilities	(38)		(79)		(38)
Fair Value, Inputs, Level 2 [Member] | Natural Gas Derivatives [Member]
Natural gas derivatives
Derivative Assets	50	[1]	67	[1]	49	[1]
Derivative Liabilities	(75)		(79)		(23)
Fair Value, Inputs, Level 2 [Member] | Interest Rate Contract [Member]
Natural gas derivatives
Derivative Assets		[1]		[1]	6	[1]
Natural Gas Derivatives [Member]
Natural gas derivatives
Derivative Assets	137	[1],[2],[3]	116	[1],[2],[3]	103	[1],[2],[3]
Derivative Liabilities	(82)	[2],[3]	(80)	[2],[3]	(24)	[2],[3]
Netting of cash collateral	69	[1]	43	[1]	40	[1]
Netting of cash collateral	$ 31		$ 78		$ 37

[1] Balances of $1 million at March 31, 2014, $3 million at December 31, 2013 and $2 million at March 31, 2013 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) for any of the dates presented.

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