Significant Accounting Policies (Narrative) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016 USD ($) customer	Dec. 31, 2015 USD ($) customer	Dec. 31, 2014 USD ($)
Significant Accounting Policies [Line Items]
Allowance for doubtful accounts	$ 3.9	$ 6.3
Estimated useful lives of intangible assets	6 years 1 month 8 days	6 years 3 months 7 days
Amount capitalized related to internal use software	$ 36.2	$ 46.2
Amount expensed related to internal use software	49.6	44.6	$ 37.3
Capitalized costs for internally developed software to be sold as a service	48.6	47.7
Amount expensed related to internally developed computer software to be sold as a service	43.9	37.2	29.5
Allowance for estimated product returns	2.0	1.4
Advertising costs	155.8	144.1	150.1
Foreign postretirement benefit plans
Significant Accounting Policies [Line Items]
Termination indemnities	13.2	13.8
Termination indemnities, compensation expense	$ 2.5	$ 3.8	$ 3.2
Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	3 years
Licensing agreement term	1 year
Minimum | License update
Significant Accounting Policies [Line Items]
Revenue recognition, period for recognition	12 months
Maximum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	7 years
Licensing agreement term	5 years
Maximum | License update
Significant Accounting Policies [Line Items]
Revenue recognition, period for recognition	24 months
Weighted average | Online service agreements
Significant Accounting Policies [Line Items]
Revenue recognition, period for recognition	12 months
Customer concentration risk | Accounts receivable
Significant Accounting Policies [Line Items]
Number of customers meeting concentration risk threshold | customer	0	0
Internal use software | Minimum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	3 years
Internal use software | Maximum
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	7 years
Internally developed software to be sold as a service
Significant Accounting Policies [Line Items]
Estimated useful lives of intangible assets	2 years