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Summary of Significant Accounting Policies - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Decrease to customer deposits	$ 2,000.0		$ 1,400.0
Effect of change on net income	$ 9.2
Effect of change on basic earnings per share (in dollars per share)	$ 0.04
Effect of change on diluted earnings per share (in dollars per share)	$ 0.04
Debt \| Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		$ 14.4
Retained Earnings \| Accounting Standards Update 2016-16
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		(6.6)
Retained Earnings \| Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		(16.9)
AOCI Attributable to Parent \| Accounting Standards Update 2017-12
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative effect of new accounting principle in period of adoption		2.5
Difference between Revenue Guidance in Effect before and after Topic 606 \| Accounting Standards Update 2014-09
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Prepaid expenses and other assets		64.6
Decrease to customer deposits		$ 64.6