Regulatory Matters - Gulf Power Regulatory Matters (Details) - Gulf Power - USD ($) $ in Millions |
1 Months Ended | 3 Months Ended | 9 Months Ended |
|---|---|---|---|
Jul. 31, 2017 |
Mar. 31, 2017 |
Dec. 31, 2018 |
|
| Schedule of Regulatory Assets and Liabilities [Line Items] | |||
| Public utilities, approved rate increase (decrease), amount | $ 54.0 | ||
| Rate case settlement annual increase base rates | 62.0 | ||
| Purchased power capacity cost recovery clause credit | $ 8.0 | ||
| Tax reform settlement agreement, annual reduction of revenue from base rates | $ 18.0 | ||
| Tax reform settlement agreement, annual reduction of revenue from environmental cost recovery rates | 16.0 | ||
| Tax reform settlement agreement, refund | $ 69.0 | ||
| Plant Scherer Unit 3 | |||
| Schedule of Regulatory Assets and Liabilities [Line Items] | |||
| Loss on Plant Scherer Unit 3 | $ 32.5 |