Introduction (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012
Leveraged Leases [Abstract]
Expected potential impairment loss on abandonment of the project	$ 90
Maximum [Member]
Leveraged Leases [Abstract]
Reduction in leveraged lease income	$ 20

Expected Reduction In Leveraged Lease Income On Successful Completion Of Project.

No definition available.

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Namespace Prefix:	so_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant