CONTINGENCIES, COMMITMENTS, AND GUARANTEES - MPC Other Matters (Details) - USD ($)		12 Months Ended				60 Months Ended
	Jan. 01, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2025	Jan. 15, 2024	Dec. 31, 2016	Dec. 31, 2010
Loss Contingencies [Line Items]
Period costs		$ 26,000,000	$ 19,000,000
Mississippi Power
Loss Contingencies [Line Items]
Period costs		0	0
Kemper County energy facility assets, net | Mississippi Power
Loss Contingencies [Line Items]
Pre-tax charge to income		11,000,000	4,000,000	$ 24,000,000
After tax charge to income		$ 8,000,000	$ 3,000,000
Government grants expected								$ 137,000,000	$ 270,000,000
Government grants received					$ 387,000,000
Scenario, Forecast | Kemper County energy facility assets, net | Mississippi Power | Minimum
Loss Contingencies [Line Items]
Period costs						$ 10,000,000
Scenario, Forecast | Kemper County energy facility assets, net | Mississippi Power | Maximum
Loss Contingencies [Line Items]
Period costs						$ 20,000,000
Scenario, Forecast | Plant Daniel | Mississippi Power
Loss Contingencies [Line Items]
Payments to acquire businesses							$ 1
Business combination, option to purchase, period							120 days
Scenario, Forecast | Plant Daniel | Gulf Power
Loss Contingencies [Line Items]
Undivided ownership interest to be restructured							50.00%
Percent ownership in individual unit							100.00%
Disposal Group, Disposed of by Sale, Not Discontinued Operations | Gulf Power
Loss Contingencies [Line Items]
Proceeds from divestiture of businesses, amount held back	$ 75,000,000