Note 5 - Derivative Instruments (Detail) - Derivative Instruments on the Condensed Consolidated Statements of Financial Position (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Designated as cash flow and fair value hedges
Total	$ 36	[1],[2]	$ 31	[1],[2]
Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Asset	1	[1],[2]	9	[1],[2]
Designated as Hedging Instrument [Member] | Noncurrent Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Asset	3	[1],[2]	0	[1],[2]
Designated as Hedging Instrument [Member] | Noncurrent Interest Rate Swap [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Asset	0	[1],[2]	13	[1],[2]
Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Liability	(2)	[1],[2]	(12)	[1],[2]
Designated as Hedging Instrument [Member] | Noncurrent Interest Rate Swap [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Liability	0	[1],[2]	(13)	[1],[2]
Designated as Hedging Instrument [Member]
Designated as cash flow and fair value hedges
Total	2	[1],[2]	(3)	[1],[2]
Not Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Asset	394	[1],[2]	706	[1],[2]
Not Designated as Hedging Instrument [Member] | Noncurrent Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Asset	45	[1],[2]	133	[1],[2]
Not Designated as Hedging Instrument [Member] | Current Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Liability	(355)	[1],[2]	(689)	[1],[2]
Not Designated as Hedging Instrument [Member] | Noncurrent Natural Gas Contracts [Member]
Designated as cash flow and fair value hedges
Derivative Fair Value Of Derivative Liability	(50)	[1],[2]	(116)	[1],[2]
Not Designated as Hedging Instrument [Member]
Designated as cash flow and fair value hedges
Total	$ 34	[1],[2]	$ 34	[1],[2]

[1] These amounts are netted within our Consolidated Statements of Financial Position for amounts which we have netting arrangements with the counterparties.

[2] As required by the authoritative guidance related to derivatives and hedging, the fair value amounts above are presented on a gross basis. As a result, the amounts do not include cash collateral held on deposit in broker margin accounts of $69 million as of December 31, 2012 and $147 million as of December 31, 2011. Accordingly, the amounts above will differ from the amounts presented on our Consolidated Statements of Financial Position and the fair value information presented for our derivative instruments in the recurring fair values table of Note 4.