New Accounting Pronouncements - Additional Information (Detail) - USD ($) $ in Millions		9 Months Ended
	Jan. 01, 2016	Sep. 30, 2015	Dec. 31, 2015
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cumulative adjustment to retained earnings	$ 2.6
Excess tax benefit reclassified from operating activities to financing activities		$ 1.5
Long-term Debt, Less Amount Due Within One Year [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Debt issuance cost			$ 27.7
Long-term Debt, Less Amount Due Within One Year [Member] | Tampa Electric Company [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Debt issuance cost			$ 18.1