Note 6 - Debt and Credit Facilities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Proceeds from Issuance of Long-term Debt	$ 500
Debt Instrument, Term	30 years
Debt Instrument, Interest Rate, Stated Percentage	4.40%
Repayments of Senior Debt	225
Long-term Debt	3,819		3,327	3,334
Derivative Asset, Notional Amount		50
Derivative, Average Swaption Interest Rate		1.98%
Proceeds from Derivative Instrument, Financing Activities	6
Refinanced [Member] | Debt Issued By New Jersey Economic Development Authority [Member] | Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt		180
Refinanced [Member] | Debt Issued by Brevard County Florida [Member] | Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt		20
Refinanced [Member] | Refunding Bonds [Member] | Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt		60
Refinanced [Member] | Purchase of Existing Bonds [Member] | Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt		140
Refinanced [Member] | Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt		200
Interest Rate Swap [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Derivative Asset, Notional Amount		300
Derivative, Average Swaption Interest Rate		1.85%
AGL Capital [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Debt, Weighted Average Interest Rate	0.40%
Gas Facility Revenue Bonds [Member]
Note 6 - Debt and Credit Facilities (Details) [Line Items]
Long-term Debt	$ 200		$ 200	$ 200