Other Comprehensive Income - Accumulated Other Comprehensive Loss (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized losses from cash flow hedges, tax benefit	$ 2.1	$ 2.3
Tampa Electric Company [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized losses from cash flow hedges, tax benefit	2.1	2.3
Pension Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Unamortized pension and other benefit loss, prior service cost (credit) and transition obligation, tax expense (benefit)	21.1	21.5
Other Postretirement Benefits [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Unamortized pension and other benefit loss, prior service cost (credit) and transition obligation, tax expense (benefit)	$ 16.0	$ 16.1