Income Tax Matters, Reconciliation of Changes in the Gross Unrecognized Tax Benefits Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of changes in the gross unrecognized tax benefits:
Gross unrecognized tax benefits at beginning of period	$ 1.8	$ 1.7	$ 2.2
Gross increases for tax positions of prior years	0.0	0.1	0.1
Gross decreases for tax positions of prior years	(0.3)	0.0	0.0
Gross decrease for tax positions relating to lapse of a statute of limitation	0.0	0.0	(0.6)
Gross unrecognized tax benefits at end of period	$ 1.5	$ 1.8	$ 1.7