Note 4 - Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012		Dec. 31, 2012
Derivative Liability, Fair Value, Net	$ (24)	[1],[2]	$ (103)	[1],[2]	$ (39)	[1],[2]
Increase (Decrease) in Risk Management Assets and Liabilities	(18)		(15)
Collateral Already Posted, Aggregate Fair Value	77		209		69
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	2
Less Than Two Years [Member] | Natural Gas [Member]
Percent Of Derivative Contracts	98.00%
ExpiringIn Two To Six Years [Member] | Natural Gas [Member]
Percent Of Derivative Contracts	2.00%
Weather Derivatives [Member]
Derivative Instruments, Loss Recognized in Income	$ 2		$ 14
Minimum [Member]
Natural Gas Derivative Term	2
Maximum [Member]
Natural Gas Derivative Term	6

[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.