Note 5 - Derivative Instruments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 06, 2012	May 04, 2011
Derivative Liability, Fair Value, Net	$ 39	$ 110
Increase (Decrease) in Risk Management Assets and Liabilities	(72)	17	(7)
Notional Amount of Interest Rate Cash Flow Hedge Derivatives				200	250
Derivative, Fixed Interest Rate				1.78%
Interest Rate Cash Flow Hedge Asset at Fair Value	3	13
Interest Rate Cash Flow Hedge Liability at Fair Value		13
Collateral Already Posted, Aggregate Fair Value	69	147
Price Risk Cash Flow Hedge Unrealized Gain (Loss) to be Reclassified During Next 12 Months	1
Less Than Two Years [Member] | Natural Gas [Member]
Percent of Derivative Contracts	99.00%
Expiring In Two To Six Years [Member] | Natural Gas [Member]
Percent of Derivative Contracts	1.00%
Weather Derivatives [Member]
Derivative Instruments, Loss Recognized in Income	14	9	27
Minimum [Member]
Natural Gas Derivative Term	3 years
Maximum [Member]
Natural Gas Derivative Term	6 years
Interest Rate Derivatives [Member]
Senior Notes					$ 300
Senior Notes Weighted Average Interest Rate					6.40%