Employee Postretirement Benefits - Schedule of Funded Status (Detail) - TECO Energy [Member] - USD ($) $ in Millions		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 659		$ 766
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation (PBO/APBO)		750		812		$ 770
Fair value of plan assets		659	[1]	766	[1]	649
Funded status at end of year		(91)		(46)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation (PBO/APBO)	[2]	173		193		175
Fair value of plan assets	[2]	0	[1]	0	[1]	$ 0
Other Postretirement Benefits [Member] | Florida [Member]
Defined Benefit Plan Disclosure [Line Items]
Benefit obligation (PBO/APBO)	[2]	173		193
Fair value of plan assets	[2]	0		0
Funded status at end of year	[2]	$ (173)		$ (193)

[1] The MRV of plan assets is used as the basis for calculating the EROA component of periodic pension expense. MRV reflects the fair value of plan assets adjusted for experience gains and losses (i.e. the differences between actual investment returns and expected returns) spread over five years.

[2] Represent amounts for TECO Energy’s Florida-based other postretirement benefit plan.