Recent Accounting Pronouncements New Accounting Standards - Cumulative Effect of changes due to Adoption of ASU 2014-09 (Details) - USD ($) $ in Millions	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets [Abstract]
Accounts receivable, net	$ 33.8	$ 27.8	$ 49.6
Income taxes receivable	0.0	(31.5)	(35.6)
Current assets of discontinued operations held for sale	0.0	69.8	69.1
Other current assets	26.4		18.9
Liabilities [Abstract]
Other assets	(17.5)	(12.5)	(13.6)
Accrued expense	83.0	76.6	75.8
Taxes Payable, Current	(0.5)		0.0
Deferred revenue	(12.8)	(52.0)	(70.9)
Current liabilities of discontinued operations held for sale	0.0	(149.4)	(188.2)
Deferred revenue	(21.1)	(24.8)	(29.3)
Deferred income taxes	(66.4)	(40.5)	(40.6)
Non-current liabilities of discontinued operations held for sale	0.0	60.3	54.8
Equity [Abstract]
Retained earnings	504.1	664.0	$ 634.3
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net	3.2	21.8
Income taxes receivable		(4.1)
Current assets of discontinued operations held for sale		0.7
Liabilities [Abstract]
Other assets	(0.5)	(1.1)
Accrued expense	0.9	0.8
Taxes Payable, Current	(0.2)
Deferred revenue	(3.9)	(18.9)
Current liabilities of discontinued operations held for sale		(38.8)
Deferred revenue	(1.3)	(4.5)
Deferred income taxes	(0.2)	(0.1)
Non-current liabilities of discontinued operations held for sale		5.5
Equity [Abstract]
Retained earnings	0.2	$ 29.7
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net	37.0
Liabilities [Abstract]
Other assets	(18.0)
Accrued expense	82.1
Taxes Payable, Current	(0.3)
Deferred revenue	(16.7)
Deferred revenue	(22.4)
Deferred income taxes	(66.2)
Equity [Abstract]
Retained earnings	$ 503.9