Note 7 - Debt and Credit Facilities (Detail) - Debt to Capitalization Ratios	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2011
AGL Capital [Member]
Debt-to-capitalization ratio	54.00%	58.00%	53.00%
Nicor Gas [Member]
Debt-to-capitalization ratio	43.00%	60.00%