Other Operating Credits and Charges, Net (Details) - USD ($) $ in Millions	3 Months Ended				9 Months Ended
	Sep. 30, 2016	Jun. 30, 2016	Sep. 30, 2015	Mar. 31, 2015	Sep. 30, 2016	Sep. 30, 2015
Other Operating Credits And Charges, Net [Abstract]
Other operating credits and charges, net	$ 0.0	$ 11.4	$ 1.0	$ 11.6	$ 11.4	$ 12.6