Employee Postretirement Benefits - Schedule of Net Periodic Benefit Cost (Detail) - USD ($) $ in Millions	3 Months Ended			6 Months Ended
	Jun. 30, 2017		Jun. 30, 2016	Jun. 30, 2017		Jun. 30, 2016
Pension Benefits [Member]
Amortization of:
Net periodic benefit cost	$ 4		$ 3	$ 7		$ 6
Other Postretirement Benefits [Member]
Amortization of:
Net periodic benefit cost	2		2	3		3
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	5		5	10		9
Interest cost	9		8	16		16
Expected return on assets	(12)		(11)	(24)		(22)
Amortization of:
Prior service (benefit) cost	0		0	0		0
Actuarial loss	4		3	8		7
Regulatory asset				0		0
Curtailment cost	0		1	0		1
Settlement cost	0	[1]	1	7	[1]	1
Net periodic benefit cost	6		7	17		12
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0		1	1		1
Interest cost	2		2	4		4
Expected return on assets	0		0	0		(1)
Amortization of:
Prior service (benefit) cost	1		(1)	0		(1)
Actuarial loss	(1)		0	(1)		0
Regulatory asset				0		1
Curtailment cost	0		0	0		0
Settlement cost	0		0	0		0
Net periodic benefit cost	$ 2		$ 2	$ 4		$ 4

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