INCOME TAXES - Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	$ 18	$ 484
Increase from current periods		10
Increase from prior periods		10
Decrease from prior periods	(18)	(196)
Reductions due to settlements		(290)
Balance at end of year	0	18
Mississippi Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	465
Increase from current periods		0
Increase from prior periods		2
Decrease from prior periods	0	(177)
Reductions due to settlements		(290)
Balance at end of year	0	0
Southern Power
Changes in unrecognized tax benefits [Roll Forward]
Unrecognized tax benefits at beginning of year	0	17
Increase from current periods		0
Increase from prior periods		0
Decrease from prior periods	0	(17)
Reductions due to settlements		0
Balance at end of year	$ 0	$ 0

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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- Definition

Amount of unrecognized tax benefits.

+ References

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Amount of decrease in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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Amount of decrease in unrecognized tax benefits resulting from settlements with taxing authorities.

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Amount of increase in unrecognized tax benefits resulting from tax positions that have been or will be taken in current period tax return.

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Amount of increase in unrecognized tax benefits resulting from tax positions taken in prior period tax returns.

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