Note 4 - Derivative Instruments (Detail) - Derivative Instruments on the Consolidated Statements of Income (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Not designated as hedges
Total (losses) gains on derivative instruments	$ (27)		$ 2
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 for settlement of hedged item			(1)
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)		2
Not Designated as Hedging Instrument [Member] | Natural Gas Contracts [Member]
Not designated as hedges
Natural gas contracts - net fair value adjustments recorded in operating revenues (1)	(24)	[1]	4	[1]
Natural gas contracts - net fair value adjustments recorded in cost of goods sold (2)		[2]	(2)	[2]
Natural gas contracts - net value adjustments recorded in operation and maintenance expense			$ (1)

[1] Associated with the fair value of existing derivative instruments at March 31, 2013 and 2012

[2] Excludes losses recorded in cost of goods sold associated with weather derivatives of $2 million for the three months ended March 31, 2013 and gains of $14 million for the three months ended March 31, 2012