Note 4 - Derivative Instruments (Detail) - Derivative Instruments on the Condensed Consolidated Statements of Financial Position (USD $) In Millions, unless otherwise specified	Mar. 31, 2013		Dec. 31, 2012		Mar. 31, 2012
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	$ 111	[1],[2]	$ 144	[1],[2]	$ 266	[1],[2]
Net amounts of assets and liabilities presented in our unaudited Condensed Consolidated Statements of Financial Position	(24)	[1],[2]	(39)	[1],[2]	(103)	[1],[2]
Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	3	[1],[2]	1	[1],[2]	5	[1],[2]
Liabilities	(1)	[1],[2]	(2)	[1],[2]	(11)	[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]
Liabilities		[1],[2]		[1],[2]		[1],[2]
Designated as Hedging Instrument [Member] | Current Interest Rate Swap Agreements [Member]
Designated as cash flow hedges and fair value hedges
Assets	5	[1],[2]		[1],[2]		[1],[2]
Liabilities		[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]	9	[1],[2]
Liabilities		[1],[2]		[1],[2]	(11)	[1],[2]
Designated as Hedging Instrument [Member]
Designated as cash flow hedges and fair value hedges
Assets	8	[1],[2]	4	[1],[2]	14	[1],[2]
Liabilities	(1)	[1],[2]	(2)	[1],[2]	(22)	[1],[2]
Not Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	332	[1],[2]	394	[1],[2]	683	[1],[2]
Liabilities	(327)	[1],[2]	(355)	[1],[2]	(718)	[1],[2]
Not Designated as Hedging Instrument [Member] | Long-Term Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	46	[1],[2]	45	[1],[2]	82	[1],[2]
Liabilities	(48)	[1],[2]	(50)	[1],[2]	(85)	[1],[2]
Not Designated as Hedging Instrument [Member]
Designated as cash flow hedges and fair value hedges
Assets	378	[1],[2]	439	[1],[2]	765	[1],[2]
Liabilities	(375)	[1],[2]	(405)	[1],[2]	(803)	[1],[2]
Long-Term Natural Gas Contracts [Member]
Designated as cash flow hedges and fair value hedges
Assets	386	[1],[2]	443	[1],[2]	779	[1],[2]
Liabilities	(376)	[1],[2]	(407)	[1],[2]	(825)	[1],[2]
Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position	(275)	[1],[2]	(299)	[1],[2]	(513)	[1],[2]
Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position	$ 352	[1],[2]	$ 368	[1],[2]	$ 722	[1],[2]

[1] 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.

[2] 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 $77 million as of March 31, 2013, $69 million as of December 31, 2012 and $209 million as of March 31, 2012. Cash collateral is included in the "Gross amounts offset in our unaudited Condensed Consolidated Statements of Financial Position" line of this table.