Consolidated Statements of Comprehensive Income - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 173.5		$ 130.4		$ 197.7
Other comprehensive income (loss), net of tax
Gain on cash flow hedges		3.5		0.7		1.4
Amortization of unrecognized benefit costs and other	[1]	2.1		(3.0)		14.8
Change in benefit obligation due to valuation		(9.8)		8.0		0.0
Increase in unrecognized postemployment costs		0.0		(8.2)	[2]	0.0
Recognized benefit costs due to settlement		7.7	[3]	0.0		1.6
Other comprehensive income (loss), net of tax		3.5		(2.5)		17.8
Comprehensive income		$ 177.0		$ 127.9		$ 215.5

[1] Related to postretirement and postemployment benefits. See Note 5 for additional information.

[2] Amounts reflect an out-of-period adjustment related to TECO Coal’s unfunded black lung liability.

[3] Related to the settlement of the TECO Coal black lung obligation at the closing of the sale. See Note 19 for additional information.