Consolidated Condensed Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2015		Sep. 30, 2014		Sep. 30, 2015		Sep. 30, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 53.2		$ 11.1		$ 123.0		$ 119.6
Other comprehensive income, net of tax
Gain on cash flow hedges		0.2		0.1		3.3		0.4
Amortization of unrecognized benefit costs	[1]	0.2		0.2		1.8		1.6
Change in benefit obligation due to valuation		(5.7)		(0.7)		(5.7)		(0.7)
Recognized cost due to settlement		7.7	[2]	0.0		7.7	[2]	0.0
Increase in unrecognized postemployment costs		0.0		0.0	[3]	0.0		(8.2)	[3]
Other comprehensive income (loss), net of tax		2.4		(0.4)		7.1		(6.9)
Comprehensive income		$ 55.6		$ 10.7		$ 130.1		$ 112.7

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

[2] Related to the settlement of the TECO Coal black lung obligation at the closing of the sale. See Notes 5 and 15 for additional information.

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