Note 6 - Employee Benefit Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2016	Dec. 31, 2015
Note 6 - Employee Benefit Plans (Details) [Line Items]
Regulatory Assets	$ 714,000,000		$ 819,000,000
Defined Benefit Plan, Funding Target	100.00%
Defined Benefit Plan, Funding Target, Amortization Period	7 years
Defined Contribution Plan, Employer Matching Contribution	17,000,000		14,000,000		12,000,000
Scenario, Forecast [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation Pension, Band Increase, Rate							0.00%	2.00%
Defined Benefit Welfare Benefits [Member] | Other Postretirement Benefit Plan [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Regulatory Assets	122,000,000		108,000,000
Supplemental Employee Retirement Plan [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Benefit Obligation	2,000,000		2,000,000
Other Postretirement Benefit Plan [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Assumptions Used Calculating Benefit Obligation Pension, Band Increase, Rate		[1]		[1]		[1]
AGL Resources Retirement Plan [Member]
Note 6 - Employee Benefit Plans (Details) [Line Items]
Defined Benefit Plan, Required Employer Contribution, Amount	$ 0		$ 0

[1] Only applicable to the Nicor Gas union employees. The pension bands for the former Nicor Plan have been updated to reflect the new negotiated rates for 2015 and 2016, of 2.0% and 0%, respectively, as indicated in the union agreement dated March 2014.