Income and Other Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefit, beginning of period	$ 2.5	$ 2.9	$ 0.6
Additions for tax positions related to the current year	0.7	0.3	0.5
Additions for tax positions of prior years	0.1	0.3	2.1
Reductions for tax positions of prior years	(0.2)	(1.0)	(0.3)
Unrecognized tax benefit, end of period	$ 3.1	$ 2.5	$ 2.9