Discontinued Operations, Assets Held for Sale and Asset Impairments - Additional Information (Detail) - TECO Coal [Member] - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2015	Dec. 31, 2014	Feb. 05, 2015
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Contingent Payments			$ 60.0
Purchase price			$ 80.0
Total pretax impairment charges	$ 78.6	$ 115.9