Employee Postretirement benefits - Schedule of Pension Plan Assets (Detail) - TECO Energy [Member]	Dec. 31, 2024	Dec. 31, 2023
Actual Asset Allocation [Member]
Asset Category
Actual Allocation, End of Year	100.00%	100.00%
Actual Asset Allocation [Member] | Cash and Cash Equivalents [Member]
Asset Category
Actual Allocation, End of Year	2.00%	3.00%
Actual Asset Allocation [Member] | Equity Securities [Member]
Asset Category
Actual Allocation, End of Year	58.00%	57.00%
Actual Asset Allocation [Member] | Fixed Income Securities [Member]
Asset Category
Actual Allocation, End of Year	40.00%	40.00%
Target Allocation [Member]
Asset Category
Target Allocation	100.00%	100.00%
Target Allocation [Member] | Cash and Cash Equivalents [Member] | Minimum [Member]
Asset Category
Target Allocation	0.00%	0.00%
Target Allocation [Member] | Cash and Cash Equivalents [Member] | Maximum [Member]
Asset Category
Target Allocation	10.00%	10.00%
Target Allocation [Member] | Equity Securities [Member] | Minimum [Member]
Asset Category
Target Allocation	48.00%	48.00%
Target Allocation [Member] | Equity Securities [Member] | Maximum [Member]
Asset Category
Target Allocation	68.00%	68.00%
Target Allocation [Member] | Fixed Income Securities [Member] | Minimum [Member]
Asset Category
Target Allocation	29.00%	29.00%
Target Allocation [Member] | Fixed Income Securities [Member] | Maximum [Member]
Asset Category
Target Allocation	49.00%	49.00%