Recent Accounting Pronouncements New Accounting Standards - Cumulative Effect of changes due to Adoption of ASU 2014-09 (Details) - USD ($) $ in Millions	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets [Abstract]
Accounts receivable, net	$ 37.3	$ 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	22.1		18.9
Liabilities [Abstract]
Other assets	(13.1)	(12.5)	(13.6)
Accrued expense	95.2	76.6	75.8
Taxes Payable, Current	(24.5)		0.0
Deferred revenue	(13.6)	(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	(48.6)	(40.5)	(40.6)
Non-current liabilities of discontinued operations held for sale	0.0	60.3	54.8
Equity [Abstract]
Retained earnings	448.1	664.0	$ 634.3
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net	0.7	21.8
Income taxes receivable		(4.1)
Current assets of discontinued operations held for sale		0.7
Liabilities [Abstract]
Other assets	(1.8)	(1.1)
Accrued expense	0.8	0.8
Taxes Payable, Current	(0.2)
Deferred revenue	(1.8)	(18.9)
Current liabilities of discontinued operations held for sale		(38.8)
Deferred revenue	(2.5)	(4.5)
Deferred income taxes	(0.2)	(0.1)
Non-current liabilities of discontinued operations held for sale		5.5
Equity [Abstract]
Retained earnings	0.6	$ 29.7
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net	38.0
Liabilities [Abstract]
Other assets	(14.9)
Accrued expense	94.4
Taxes Payable, Current	(24.3)
Deferred revenue	(15.4)
Deferred revenue	(23.6)
Deferred income taxes	(48.4)
Equity [Abstract]
Retained earnings	$ 447.5