Recent Accounting Pronouncements New Accounting Standards - Cumulative Effect of changes due to Adoption of ASU 2014-09 (Details) - USD ($) $ in Millions	Mar. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets [Abstract]
Accounts receivable, net of allowance for doubtful accounts of $3.9 at March 31, 2018 and $3.6 at December 31, 2017	$ (34.6)	$ (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	26.0		18.9
Liabilities [Abstract]
Other assets	(12.5)	(12.5)	(13.6)
Accrued expense	75.6	76.6	75.8
Deferred revenue	(91.5)	(52.0)	(70.9)
Current liabilities of discontinued operations held for sale	0.0	(149.4)	(188.2)
Deferred revenue	(25.0)	(24.8)	(29.3)
Deferred income taxes	43.8	40.7	40.6
Non-current liabilities of discontinued operations held for sale	0.0	60.7	54.8
Equity [Abstract]
Retained earnings	344.5	663.4	$ 634.3
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net of allowance for doubtful accounts of $3.9 at March 31, 2018 and $3.6 at December 31, 2017	(3.1)	(21.8)
Income taxes receivable		(4.1)
Current assets of discontinued operations held for sale		0.7
Liabilities [Abstract]
Other assets	(2.0)	(1.1)
Accrued expense	0.8	0.8
Deferred revenue	(0.2)	(18.9)
Current liabilities of discontinued operations held for sale		(38.8)
Deferred revenue	(4.3)	(4.5)
Deferred income taxes	0.1	0.1
Non-current liabilities of discontinued operations held for sale		5.9
Equity [Abstract]
Retained earnings	(1.5)	$ 29.1
Calculated under Revenue Guidance in Effect before Topic 606 [Member]
Assets [Abstract]
Accounts receivable, net of allowance for doubtful accounts of $3.9 at March 31, 2018 and $3.6 at December 31, 2017	(37.7)
Liabilities [Abstract]
Other assets	(14.5)
Accrued expense	74.8
Deferred revenue	(91.7)
Deferred revenue	(29.3)
Deferred income taxes	43.7
Equity [Abstract]
Retained earnings	$ 346.0