Employee Postretirement Benefits - Additional Information (Detail) - USD ($)			6 Months Ended	12 Months Ended				24 Months Ended
		Jan. 02, 2017	Dec. 31, 2016	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	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					110.60%	112.50%
Employer contributions					$ 8,000,000	$ 36,000,000
Employer contributions in next fiscal year					$ 15,000,000
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. During the period of January 2015 to December 2016, the employer matching contributions were 70% of eligible participant contributions with additional incentive match of up to 30% 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	$ 8,000,000
Employer matching contribution percentage of eligible participant contribution		75.00%					70.00%	70.00%
Defined benefit plan additional percentage of eligible compensation for matching contributions by employer					25.00%			30.00%
Non-qualified SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, assets					$ 14,000,000	17,000,000
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					16,000,000	14,000,000	$ 13,000,000
Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year					12,000,000
Increase in net periodic benefit cost			$ 1,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost					8,000,000	6,000,000	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]
Employer contributions					0	0	0
Benefits paid					7,000,000
Expected payment in next twelve months					5,000,000
SERP [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected settlement charge				$ 1,000,000
Restoration Plan [Member] | Scenario Forecast [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected settlement charge				$ 1,000,000
TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation of defined benefit pension plans					$ 705,000,000	762,000,000
Percentage of defined benefit plan's actual earned losses					8.00%
Defined contribution plan, maximum employer match percentage					6.00%
TECO Energy [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated annual contributions					$ 17,000,000
TECO Energy [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Estimated annual contributions					14,000,000
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost					22,000,000	27,000,000	22,000,000
Curtailment loss					0	0	1,000,000
Settlement charge					(2,000,000)	(7,000,000)	(1,000,000)
Commitments			770,000,000		750,000,000	812,000,000	770,000,000	$ 770,000,000
Employer contributions					10,000,000	46,000,000
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost					8,000,000	7,000,000	7,000,000
Curtailment loss					0	0	0
Settlement charge					0	0	0
Commitments	[1]		$ 175,000,000		173,000,000	193,000,000	$ 175,000,000	$ 175,000,000
Employer contributions	[1]				0	0
Employer contributions in next fiscal year					10,000,000
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

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