Note 4 - Fair Value Measurements (Detail) - Amortized Cost and Fair Value of Long-Term Debt (USD $) In Millions, unless otherwise specified	Mar. 31, 2012		Dec. 31, 2011		Mar. 31, 2011
Long-term debt amortized cost (1)	$ 3,573	[1]	$ 3,576	[1]	$ 2,173	[1]
Long-term debt fair value (1) (2)	$ 3,922	[1],[2]	$ 3,938	[1],[2]	$ 2,304	[1],[2]

[1] March 31, 2012 and December 31, 2011 include $15 million of medium-term notes that are due in 2012 and the debt assumed in the Nicor merger with a carrying value of $500 million,.

[2] Valued using Level 2 inputs.