Discontinued Operations and Asset Impairments - Additional Information (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Sep. 21, 2015
TECO Coal [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Contingent payments	$ 0	$ 60

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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