Note 5 - Derivative Instruments (Detail) - Derivative Instruments on the Consolidated Statements of Income (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Designated as cash flow hedges
Total gains (losses) on derivative instruments	$ 24		$ 33		$ (19)
Designated as Hedging Instrument [Member] | Natural Gas Contracts [Member]
Designated as cash flow hedges
Natural gas contracts - loss reclassified from OCI into cost of goods sold	(3)		(6)		(16)
Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Designated as cash flow hedges
Interest rate swaps - ineffectiveness recorded as an offset to interest expense	(3)		3		0
Not Designated as Hedging Instrument [Member] | Natural Gas Contracts [Member]
Designated as cash flow hedges
Natural gas contracts - net fair value adjustments recorded in operating revenues (1)	34	[1]	40	[1]	(1)	[1]
Natural gas contracts - net fair value adjustments recorded in cost of goods sold (2)	0	[2]	0	[2]	(2)	[2]
Natural gas contracts - net fair value adjustments recorded in operation and maintenance expense	$ (4)		$ (4)		$ 0

[1] Associated with the fair value of existing derivative instruments at December 31, 2012, 2011 and 2010.

[2] Excludes losses recorded in cost of goods sold associated with weather derivatives of $14 million for the year ended December 31, 2012, $9 million for the year ended December 31, 2011 and $27 million for the year ended December 31, 2010.