Retirement Benefits (Details 10)	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Pension Plans [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Fixed income, Target	23.00%
Fixed income	23.00%	22.00%
Special situations, Target	3.00%
Special Situations	0.00%	0.00%
Real estate investments, Target	14.00%
Real estate investments	14.00%	13.00%
Total Target	100.00%
Total	100.00%	100.00%
Pension Plans [Member] \| Domestic [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	26.00%
Defined Benefit Plan, Equity Securities	29.00%	29.00%
Pension Plans [Member] \| International [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	25.00%
Defined Benefit Plan, Equity Securities	25.00%	27.00%
Pension Plans [Member] \| Private equity [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	9.00%
Defined Benefit Plan, Equity Securities	9.00%	9.00%
Other Postretirement Benefits [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Special situations, Target	1.00%
Special Situations	0.00%	0.00%
Real estate investments, Target	5.00%
Real estate investments	5.00%	4.00%
Total Target	100.00%
Total	100.00%	100.00%
Other Postretirement Benefits [Member] \| Domestic [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	41.00%
Defined Benefit Plan, Equity Securities	39.00%	40.00%
Fixed income, Target	30.00%
Fixed income	31.00%	29.00%
Other Postretirement Benefits [Member] \| International [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	17.00%
Defined Benefit Plan, Equity Securities	18.00%	21.00%
Fixed income, Target	3.00%
Fixed income	4.00%	3.00%
Other Postretirement Benefits [Member] \| Private equity [Member]
Composition of Pension plan and other postretirement plan assets along with the targeted mix of assets
Defined Benefit Plan, Equity Securities, Target	3.00%
Defined Benefit Plan, Equity Securities	3.00%	3.00%

Defined benefit plan target allocation percentage of assets.

No definition available.

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Namespace Prefix:	so_
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Period Type:	instant

- Definition

The percentage of the fair value of debt securities to the fair value of total plan assets held as of the measurement date.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(1)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(1)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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Period Type:	instant

- Definition

The percentage of the fair value of equity securities to the fair value of total plan assets held as of the measurement date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The percentage of the fair value of investments other than debt securities, equity securities, and real estate to the fair value of total plan assets held as of the measurement date.

+ References

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	instant

- Definition

The percentage of the fair value of real estate to the fair value of total plan assets held as of the measurement date.

+ References

+ Details

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Balance Type:	na
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- Definition

Target allocation percentage of investments in debt securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 132R

-Paragraph 5

-Subparagraph d(2)

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 5

-Subparagraph (c)(i)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e2446-114920

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (d)(i)

-URI http://asc.fasb.org/extlink&oid=6962843&loc=d3e1928-114920

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
Period Type:	duration

- Definition

Target allocation percentage of investments in equity securities to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Target allocation percentage in other than debt securities, equity securities, and real estate to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	na
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- Definition

Target allocation percentage of investments in real estate to total plan assets presented on a weighted-average basis as of the measurement date of the latest statement of financial position.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
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- Definition

The aggregate percentage of the fair value of investments (categorized by debt securities, equity securities, real estate and other plan assets) to the fair value of total plan assets held as of the measurement date.

+ References

+ Details

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- Details

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