Fair Value Measurements - Financial Instruments for which Carrying Amount did not Equal Fair Value (Details) $ in Millions	Jun. 30, 2017 USD ($)
Southern Company
Long-term debt:
Carrying Amount	$ 46,631
Fair Value	48,228
ALABAMA POWER CO
Long-term debt:
Carrying Amount	7,440
Fair Value	8,041
GEORGIA POWER CO
Long-term debt:
Carrying Amount	10,888
Fair Value	11,585
GULF POWER CO
Long-term debt:
Carrying Amount	1,292
Fair Value	1,336
MISSISSIPPI POWER CO
Long-term debt:
Carrying Amount	2,125
Fair Value	2,071
SOUTHERN POWER CO
Long-term debt:
Carrying Amount	5,725
Fair Value	5,878
SOUTHERN Co GAS
Long-term debt:
Carrying Amount	5,699
Fair Value	$ 6,031

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant