Commitments - Estimated Long-term obligations under these commitments (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Minimum Lease Payments, Operating Leases [Abstract]
2013	$ 113.0
2014	95.0
2015	53.0
2016	45.0
2017	32.0
2018	84.0
Total	422.0
Alabama Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	20.0
2014	12.0
2015	8.0
2016	9.0
2017	4.0
2018	9.0
Total	62.0
Gulf Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	18.9
2014	17.5
2015	1.2
2016	1.0
2017	1.1
2018	0
Total	39.7
Purchased Power [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2013	164.0
2014	200.0
2015	249.0
2016	258.0
2017	263.0
2018 and thereafter	2,369.0
Total	3,503.0
Purchased Power [Member] \| Alabama Power [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2013	31.0
2014	37.0
2015	38.0
2016	39.0
2017	40.0
2018 and thereafter	223.0
Total	408.0
Purchased Power [Member] \| Gulf Power [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2013	24.7
2014	52.9
2015	78.6
2016	78.7
2017	78.8
2018 and thereafter	428.1
Total	741.8
Other Capital Lease Payments [Member]
Recorded Unconditional Purchase Obligation, Fiscal Year Maturity Schedule [Abstract]
2013	24.0
2014	19.0
2015	11.0
2016	11.0
2017	8.0
2018 and thereafter	69.0
Total	142.0
Railcars [Member] \| Alabama Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	16.0
2014	10.0
2015	8.0
2016	8.0
2017	4.0
2018	9.0
Total	55.0
Vehicles And Other [Member] \| Alabama Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	4.0
2014	2.0
2015	0
2016	1.0
2017	0
2018	0
Total	7.0
Barges and Rail Cars [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	71.0
2014	57.0
2015	24.0
2016	19.0
2017	11.0
2018	11.0
Total	193.0
Barges and Rail Cars [Member] \| Gulf Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	18.6
2014	17.2
2015	1.1
2016	0.9
2017	1.0
2018	0
Total	38.8
Other Capital Lease Payments [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	42.0
2014	38.0
2015	29.0
2016	26.0
2017	21.0
2018	73.0
Total	229.0
Other Capital Lease Payments [Member] \| Gulf Power [Member]
Minimum Lease Payments, Operating Leases [Abstract]
2013	0.3
2014	0.3
2015	0.1
2016	0.1
2017	0.1
2018	0
Total	$ 0.9

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Amount of required minimum rental payments for leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the fifth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the forth fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of required minimum rental payments maturing in the third fiscal year following the latest fiscal year for operating leases having an initial or remaining non-cancelable letter-terms in excess of one year.

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Amount of the recorded unconditional purchase obligation maturing in the fourth fiscal year following the latest fiscal year.

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Amount of the recorded unconditional purchase obligation maturing in the second fiscal year following the latest fiscal year.

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Amount of the recorded unconditional purchase obligation maturing in the third fiscal year following the latest fiscal year.

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Amount of the recorded unconditional purchase obligation maturing in the next fiscal year following the latest fiscal year.

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