Employee Postretirement Benefits - Additional Information (Detail) - USD ($)			6 Months Ended	12 Months Ended			24 Months Ended
		Jan. 02, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Percentage of tax-free subsidy under prescription drug programs				28.00%
Amortization period of Regulatory Asset				12 years
Tax of premiums paid for retiree medical benefits plan				40.00%
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 5 business days.
Primary provisions for pension benefits				First, for plans funded less than 100%, required shortfall contributions will be based on a percentage of the funding target until 2013, rather than the funding target of 100%.
Percentage of qualified pension plan's actuarial value of assets			118.10%	117.90%	118.10%		118.10%
Employer contributions				$ 36,000,000	$ 31,000,000
Employer contributions in next fiscal year				$ 37,000,000
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	$ 8,000,000	$ 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			$ 41,000,000	$ 17,000,000	$ 41,000,000		$ 41,000,000
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				14,000,000	13,000,000	14,000,000
Defined benefit plan net loss that will be amortized from regulatory assets in next fiscal year				14,000,000
Increase in net periodic benefit cost			1,000,000
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost				6,000,000	6,000,000	6,000,000
Other postretirement benefit plans service benefit to be amortized from regulatory assets in next fiscal year				0
Increase in net periodic benefit cost			0
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Employer contributions				0	0	15,000,000
TECO Energy [Member]
Defined Benefit Plan Disclosure [Line Items]
Accumulated benefit obligation of defined benefit pension plans			724,000,000	$ 762,000,000	724,000,000		724,000,000
Percentage of defined benefit plan's assets increased				19.00%
Defined contribution plan, maximum employer match percentage				6.00%
TECO Energy [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions				$ 17,000,000
TECO Energy [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Range of estimated annual contributions				6,000,000
TECO Energy [Member] | Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost				27,000,000	22,000,000	23,000,000
Curtailment loss				0	1,000,000	0
Settlement charge				(7,000,000)	(1,000,000)	0
Commitments			770,000,000	812,000,000	770,000,000	733,000,000	770,000,000
Employer contributions				46,000,000	38,000,000
TECO Energy [Member] | Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Net periodic benefit cost				7,000,000	7,000,000	6,000,000
Curtailment loss				0	0	0
Settlement charge				0	0	0
Commitments	[1]		$ 175,000,000	193,000,000	175,000,000	$ 172,000,000	$ 175,000,000
Employer contributions	[1]			(3,000,000)	$ (3,000,000)
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.