Discontinued Operations, Assets Held for Sale and Asset Impairments - Additional Information (Detail) (TECO Coal [Member], USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014	Feb. 05, 2015
TECO Coal [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Contingent Payments			$ 60,000,000
Purchase price			80,000,000
Total pretax impairment charges	$ 0	$ 115,900,000