Contingencies and Regulatory Matters - Textual - SO Regulatory Matters GULF (Details)			3 Months Ended	6 Months Ended	12 Months Ended					30 Months Ended
	Jan. 01, 2018 MW	Jul. 01, 2017	Mar. 31, 2017 MW	Jun. 30, 2017 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2019 USD ($)
Schedule of Regulatory Assets and Liabilities [Line Items]
Other cost of removal obligations						$ 2,684,000,000	$ 2,748,000,000
GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Other cost of removal obligations						221,000,000	249,000,000
Reduction in depreciation expense				$ 34,000,000			0	$ 20,100,000	$ 8,400,000
Retail rate of return on common equity		10.25%
Retail regulatory equity ratio		0.525
Loss on Plant Scherer Unit 3						$ 33,000,000	$ 0	$ 0
Settlement Agreement | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Other cost of removal obligations				$ 62,500,000
Scenario, Forecast | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Increase retail base rate, cost recovery credit										$ 8,000,000
Retail regulatory equity ratio					0.535
Rate case settlement annual reduction base rates					$ 18,200,000
Rate case settlement annual reduction environmental cost recovery rate					15,600,000
Tax reform settlement refund					$ 69,400,000
Minimum | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail rate of return on common equity		9.25%
Maximum | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail rate of return on common equity		11.25%
Plant Smith Units 1 and 2 | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units written down | MW			205
Subsequent Event | Plant Smith Units 1 and 2 | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Capacity of units approved for decertification | MW	357
Capacity of units approved for decertification, amortization period	15 years