Income Tax Matters, Reconciliation of Changes in the Gross Unrecognized Tax Benefits Table (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of changes in the gross unrecognized tax benefits:
Gross unrecognized tax benefits at beginning of period	$ 1.5	$ 1.8	$ 1.7
Gross increases for tax positions of prior years	0.0	0.0	0.1
Gross decreases for tax positions of prior years		(0.3)	0.0
Gross unrecognized tax benefits at end of period	$ 1.5	$ 1.5	$ 1.8