Contingencies and Regulatory Matters - Textual - GULF (Details)				1 Months Ended	3 Months Ended	6 Months Ended	12 Months Ended					30 Months Ended
	Jan. 01, 2018 MW	Jul. 01, 2017	Apr. 04, 2017 intervenor	Jan. 31, 2018 USD ($)	Mar. 31, 2017 USD ($) 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 ($)	Aug. 29, 2016 USD ($)
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]
Environmental exit costs, assets previously disposed, liability for remediation								52,000,000	44,000,000
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
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue								10.00%
Purchased power over (under) recovered balance percentage								10.00%
Period of establishment of conservation goals in years								5 years
Period numeric conservation goals cover in years								10 years
Regulatory asset													$ 63,000,000
Regulatory asset deferral period								15 years
Under Recovered Regulatory Clause Revenues and Other Current Liabilities | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation								$ 5,000,000	4,000,000
Other regulatory assets, deferred and other deferred credits and liabilities | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Environmental exit costs, assets previously disposed, liability for remediation								47,000,000	40,000,000
Other regulatory liabilities current | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered fuel balance								(22,000,000)	15,000,000
Over recovered energy conservation costs									4,000,000
Under recovered regulatory clause revenues | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Over (under) recovered fuel balance								(2,000,000)
Over (under) recovered environmental cost								$ 11,000,000	$ 8,000,000	$ 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, net customer impact												$ 54,300,000
Increase retail base rate, annual base revenue												62,000,000
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%
Projected fuel cost over or under recovery threshold, as a percentage of projected fuel revenue								10.00%
Maximum | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Retail rate of return on common equity		11.25%
Plant Scherer Unit 3 [Member] | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Number of Intervenors | intervenor			3
Loss on Plant Scherer Unit 3					$ 32,500,000
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 | GULF POWER CO
Schedule of Regulatory Assets and Liabilities [Line Items]
Public utilities, approved rate increase (decrease), amount				$ 63,000,000
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