Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017		Mar. 31, 2016
Pension Benefits [Member]
Amortization of:
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	$ 3		$ 3
Other Postretirement Benefits [Member]
Amortization of:
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	1		2
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5		5
Interest cost	7		8
Expected return on assets	(12)		(11)
Amortization of:
Prior service (benefit) cost	0		0
Actuarial loss	4		3
Settlement cost	7	[1]	0
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	11		5
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	1		1
Interest cost	2		2
Expected return on assets	0		0
Amortization of:
Prior service (benefit) cost	(1)		(1)
Actuarial loss	0		0
Settlement cost	0		0
Net pension expense recognized in the TECO Energy Consolidated Condensed Statements of Income	$ 2		$ 2

[1] Represents TECO Energy’s SERP settlement charge as a result of retirements that occurred subsequent to the Merger with Emera.