Consolidated Condensed Statements of Comprehensive Income (Unaudited) - USD ($) $ in Millions		3 Months Ended			6 Months Ended
		Jun. 30, 2015	Jun. 30, 2014		Jun. 30, 2015	Jun. 30, 2014
Statement Of Income And Comprehensive Income [Abstract]
Net income		$ 11.8	$ 58.4		$ 69.8	$ 108.5
Other comprehensive income, net of tax
Gain on cash flow hedges		2.8	0.1		3.1	0.3
Amortization of unrecognized benefit costs	[1]	1.0	0.5		1.6	1.0
Increase in unrecognized postemployment costs		0.0	0.0	[2]	0.0	(8.2)	[2]
Other comprehensive income (loss), net of tax		3.8	0.6		4.7	(6.9)
Comprehensive income		$ 15.6	$ 59.0		$ 74.5	$ 101.6

[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.