Fair Value Measurements - Fair Value, Nature and Risk of Investments (Details) - Private equity [Member] - USD ($)	Dec. 31, 2015	Dec. 31, 2014
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	$ 17,000,000	$ 3,000,000
Unfunded Commitments	28,000,000	7,000,000
Alabama Power [Member]
Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments
Fair Value	17,000,000	3,000,000
Unfunded Commitments	$ 28,000,000	$ 7,000,000

Fair value measurements of investments calculated at net asset value per share as well as the nature and risk of those investments.

No definition available.

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- Definition

Fair value of investments in certain entities that calculate net asset value per share, including, but not limited to, by unit, membership interest, or other ownership interest. Investments include, but are not limited to, investments in certain hedge funds, venture capital funds, private equity funds, real estate partnerships or funds.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=SL6742756-110258

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- Definition

The amount of unfunded commitments for which the entity is obligated, to those certain investments for which net asset value per share is calculated (including by unit, membership interest, or other equity (ownership interest) unit measure) (alternative investments).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 6A
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=SL6742756-110258

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