Note 8 - Debt and Credit Facilities (Detail) - Senior Note Issuances (USD $) In Millions, unless otherwise specified		12 Months Ended
	May 31, 2011	Dec. 31, 2011 Public Offering March 16, 2011 [Member]		Dec. 31, 2011 Public Offering September 15, 2011 #1 [Member]		Dec. 31, 2011 Public Offering September 15, 2011 #2 [Member]		Dec. 31, 2011 Private Placement Series A [Member]		Dec. 31, 2011 Private Placement Series B [Member]
Issuance date		Mar. 16, 2011	[1]	Sep. 15, 2011	[2]	Sep. 15, 2011	[2]	Oct. 27, 2011	[2]	Oct. 27, 2011	[2]
Amount (in Dollars)	$ 300	$ 500	[1]	$ 200	[2]	$ 300	[2]	$ 120	[2]	$ 155	[2]
Maturity date		Mar. 15, 2041	[1]	Mar. 15, 2041	[2]	Sep. 15, 2021	[2]	Oct. 27, 2016	[2]	Oct. 27, 2018	[2]
Interest rate	6.40%	5.90%	[1]	5.90%	[2]	3.50%	[2]	1.90%	[2]	3.50%	[2]

[1] The net proceeds were used to repay our commercial paper and to repay our $300 million in senior notes that matured on January 14, 2011. The remaining proceeds were used for the cash consideration and expenses incurred in connection with the Nicor merger.

[2] The net proceeds were used to pay a portion of the cash consideration and expenses incurred in connection with the Nicor merger.