Employee Postretirement Benefits - Additional Information (Detail) - USD ($)			12 Months Ended
		Jan. 02, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Redemption frequency description			The redemption frequency of the funds ranges from daily to weekly and the redemption notice period ranges from 1 business day to 30 business days.
Percentage of qualified pension plan's actuarial value of assets			108.80%	109.50%
Employer contributions			$ 15,000,000	$ 8,000,000
Employer contributions in next fiscal year			$ 16,000,000
Description of defined contribution plan			Effective January 1, 2017, the employer matching contributions increased from 70% to 75% with an additional incentive match of up to 25% of eligible participant contributions based on the achievement of certain operating company financial goals.
Defined contribution plan cost recognized			$ 11,000,000	11,000,000	$ 11,000,000
Employer matching contribution percentage of eligible participant contribution		75.00%				70.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer			25.00%
Non-qualified SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assets			$ 10,000,000	14,000,000
Unfunded [Member]
Defined Benefit Plan Disclosure [Line Items]
Commitments			0
Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Effect on net periodic benefit cost			1,000,000
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost			12,000,000	16,000,000	14,000,000
Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year			18,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost			7,000,000	8,000,000	6,000,000
Other postretirement benefit plans service benefit to be amortized from regulatory assets in next fiscal year			0
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected settlement charge			1,000,000	1,000,000
Employer contributions			0	0	0
Benefits paid			5,000,000	7,000,000
Expected payment in next twelve months			1,000,000
Restoration Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected settlement charge			1,000,000
Non Elective Employer Contribution [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined contribution plan cost recognized			1,000,000
TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation of defined benefit pension plans			$ 801,000,000	705,000,000
Percentage of defined benefit plan's actual earned returns			26.00%
Defined contribution plan, maximum employer match percentage			6.00%
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost			$ 17,000,000	22,000,000	27,000,000
Settlement charge			(1,000,000)	(2,000,000)	(7,000,000)
Commitments			843,000,000	750,000,000	812,000,000
Employer contributions			20,000,000	10,000,000
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost			7,000,000	8,000,000	7,000,000
Settlement charge			0	0	0
Commitments	[1]		180,000,000	173,000,000	193,000,000
Employer contributions	[1]		0	$ 0
Employer contributions in next fiscal year			11,000,000
TECO Energy [Member] | SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Settlement charge					$ 7,000,000
TECO Energy [Member] | Other Postretirement Benefits Florida-Based Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Other postretirement benefit plans service benefit to be amortized from regulatory assets in next fiscal year			$ 0
International Brotherhood of Electrical Workers [Member]
Defined Benefit Plan Disclosure [Line Items]
Percentage of employees represented			24.00%

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