Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2018		Jun. 30, 2017	Jun. 30, 2018		Jun. 30, 2017
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 6		$ 4	$ 9		$ 7
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	2		2	4		3
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	6		5	11		10
Interest cost	7		9	14		16
Expected return on assets	(12)		(12)	(24)		(24)
Amortization of:
Prior service (benefit) cost	0		0	0		0
Actuarial (gain) loss	4		4	9		8
Settlement cost	2	[1]	0	2	[1]	7	[2]
Net periodic benefit cost	7		6	12		17
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0		0	1		1
Interest cost	2		2	4		4
Expected return on assets	0		0	0		0
Amortization of:
Prior service (benefit) cost	1		1	0		0
Actuarial (gain) loss	(1)		(1)	(1)		(1)
Settlement cost	0		0	0		0
Net periodic benefit cost	$ 2		$ 2	$ 4		$ 4

[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.