Note 6 - Debt and Credit Facilities (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2012
Long-term Debt	$ 3,324	$ 3,327	$ 3,558
Notional Amount of Interest Rate Derivatives	50
Derivative, Average Swaption Interest Rate	1.98%
Refinanced [Member] | Refunding Bonds [Member] | Gas Facility Revenue Bonds [Member]
Long-term Debt	60
Refinanced [Member] | Purchase of Existing Bonds [Member] | Gas Facility Revenue Bonds [Member]
Long-term Debt	140
Refinanced [Member] | Gas Facility Revenue Bonds [Member] | Debt Issued By New Jersey Economic Development Authority [Member]
Long-term Debt	180
Refinanced [Member] | Gas Facility Revenue Bonds [Member] | Debt Issued by Brevard County Florida [Member]
Long-term Debt	20
Refinanced [Member] | Gas Facility Revenue Bonds [Member]
Long-term Debt	200
Interest Rate Swap [Member]
Notional Amount of Interest Rate Derivatives	300
Derivative, Average Swaption Interest Rate	1.85%
AGL Capital [Member]
Debt, Weighted Average Interest Rate	0.50%
Gas Facility Revenue Bonds [Member]
Long-term Debt	$ 200	$ 200	$ 200