Mergers and Acquisitions - After tax Transaction and Integration Charges Recognized Upon Closing of Acquisition and Included Consolidated Statements of Operations (Detail) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Total accounting charges	$ 17.0
TECO Energy [Member]
Business Acquisition [Line Items]
Legal and other consultants	0.5	$ 8.0
Bridge loan costs	0.0	3.3
Severance and relocation costs	1.0	2.8
Other costs and tax benefit	0.4	(5.5)
Total accounting charges	$ 1.9	$ 8.6

This element represents acquisition-related costs incurred to effect a business combination which costs have been expensed during the period. Such costs include finder's fees; advisory, legal, accounting, valuation, and other professional or consulting fees; general administrative costs, including the costs of maintaining an internal acquisitions department; and may include costs of registering and issuing debt and equity securities.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 25
-Paragraph 23
-URI http://asc.fasb.org/extlink&oid=34752592&loc=d3e1043-128460

Name:	us-gaap_BusinessCombinationAcquisitionRelatedCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration