Note 2 - Significant Accounting Policies and Methods of Application (Detail) - Depreciation Expense	12 Months Ended
	Dec. 31, 2012		Dec. 31, 2011		Dec. 31, 2010
Atlanta Gas Light [Member]
Depreciation Expense	2.60%	[1]	2.60%	[1]	2.50%	[1]
Chattanooga Gas [Member]
Depreciation Expense	2.50%	[1]	2.50%	[1]	2.80%	[1]
Elizabethtown Gas [Member]
Depreciation Expense	2.40%	[2]	2.50%	[2]	2.40%	[2]
Elkton Gas [Member]
Depreciation Expense	2.40%	[2]	2.40%	[2]	2.30%	[2]
Florida City Gas [Member]
Depreciation Expense	3.90%	[2]	3.90%	[2]	3.70%	[2]
Nicor Gas [Member]
Depreciation Expense	4.10%	[2]	4.10%	[2]		[2]
Virginia Natural Gas [Member]
Depreciation Expense	2.50%	[1]	2.50%	[1]	3.00%	[1]

[1] Average composite straight-line depreciation rates for depreciable property, excluding transportation equipment, which may be depreciated in excess of useful life and recovered in rates.

[2] Composite straight-line depreciation rates.