Note 4 - Derivative Instruments (Details) - Derivative Instruments on the Condensed Consolidated Statements of Financial Position (USD $) In Millions, unless otherwise specified	Sep. 30, 2013		Dec. 31, 2012		Sep. 30, 2012		Dec. 31, 2011
Designated as cash flow hedges and fair value hedges
Net amounts of assets and liabilities presented in our unaudited Condensed Consolidated Statements of Financial Position	$ 112	[1],[2]	$ 144	[1],[2]	$ 159	[1],[2]	$ 288	[1],[2]
Net amounts of assets and liabilities presented in our unaudited Condensed Consolidated Statements of Financial Position	(44)	[1],[2]	(39)	[1],[2]	(42)	[1],[2]	(110)	[1],[2]
Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	6	[1],[2]	1	[1],[2]	4	[1],[2]	9	[1],[2]
Liabilities	(5)	[1],[2]	(2)	[1],[2]	(3)	[1],[2]	(12)	[1],[2]
Designated as Hedging Instrument [Member] | Long-Term Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets		[1],[2]	3	[1],[2]		[1],[2]		[1],[2]
Liabilities		[1],[2]		[1],[2]		[1],[2]		[1],[2]
Designated as Hedging Instrument [Member] | Long-Term Interest Rate Swap Agreements [Member]
Designated as cash flow hedges and fair value hedges
Assets		[1],[2]		[1],[2]		[1],[2]	13	[1],[2]
Liabilities		[1],[2]		[1],[2]		[1],[2]	(13)	[1],[2]
Designated as Hedging Instrument [Member]
Designated as cash flow hedges and fair value hedges
Assets	6	[1],[2]	4	[1],[2]	4	[1],[2]	22	[1],[2]
Liabilities	(5)	[1],[2]	(2)	[1],[2]	(3)	[1],[2]	(25)	[1],[2]
Not Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	445	[1],[2]	394	[1],[2]	427	[1],[2]	706	[1],[2]
Liabilities	(462)	[1],[2]	(355)	[1],[2]	(408)	[1],[2]	(689)	[1],[2]
Not Designated as Hedging Instrument [Member] | Long-Term Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	143	[1],[2]	45	[1],[2]	54	[1],[2]	133	[1],[2]
Liabilities	(153)	[1],[2]	(50)	[1],[2]	(50)	[1],[2]	(116)	[1],[2]
Not Designated as Hedging Instrument [Member]
Designated as cash flow hedges and fair value hedges
Assets	588	[1],[2]	439	[1],[2]	481	[1],[2]	839	[1],[2]
Liabilities	(615)	[1],[2]	(405)	[1],[2]	(458)	[1],[2]	(805)	[1],[2]
Long-Term Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	594	[1],[2]	443	[1],[2]	485	[1],[2]	861	[1],[2]
Liabilities	(620)	[1],[2]	(407)	[1],[2]	(461)	[1],[2]	(830)	[1],[2]
Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position	(482)	[1],[2]	(299)	[1],[2]	(326)	[1],[2]	(573)	[1],[2]
Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position	$ 576	[1],[2]	$ 368	[1],[2]	$ 419	[1],[2]	$ 720	[1],[2]

[1] As required by the authoritative guidance related to derivatives and hedging, the gross amounts of recognized assets and liabilities above do not include cash collateral held on deposit in broker margin accounts of $94 million as of September 30, 2013, $69 million as of December 31, 2012, $93 million as of September 30, 2012 and $147 million as of December 31, 2011. Cash collateral is included in the "Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position" line of this table.

[2] The gross amounts of recognized assets and liabilities are netted within our unaudited Condensed Consolidated Statements of Financial Position to the extent that we have netting arrangements with the counterparties.