Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018		Sep. 30, 2017
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 4	$ 3	$ 9		$ 10
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	2	1	6		4
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5	5	16		15
Interest cost	8	8	22		24
Expected return on assets	(13)	(12)	(37)		(36)
Amortization of:
Actuarial (gain) loss	5	4	14		12
Settlement cost			2	[1]	7	[2]
Net periodic benefit cost	5	5	17		22
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0	0	1		1
Interest cost	1	2	5		6
Expected return on assets	0	0	0		0
Amortization of:
Actuarial (gain) loss	1	(1)	0		(2)
Settlement cost			0		0
Net periodic benefit cost	$ 2	$ 1	$ 6		$ 5

[1] Represents TECO Energy’s SERP and Restoration Plan settlement charges as a result of the retirements of certain executives.

[2] Represents TECO Energy’s SERP settlement charge as a result of retirements that occurred subsequent to the Merger with Emera. The charge did not impact TEC’s financial statements.