Note 4 - Fair Value Measurements (Detail) - Amortized Cost and Fair Value of Long-Term Debt (USD $) In Millions, unless otherwise specified	Dec. 31, 2012		Dec. 31, 2011
Long-term debt amortized cost, including current portions of long-term debt and capital leases (1)	$ 3,553	[1]	$ 3,578	[1]
Long-term debt fair value (1) (2)	$ 4,057	[1],[2]	$ 3,938	[1],[2]

[1] Includes the debt assumed in the Nicor merger with a carrying value of $590 million as of December 31, 2012 and $599 million as of December 31, 2011.

[2] Valued using Level 2 inputs.