Annual report pursuant to Section 13 and 15(d)

Basis of Presentation - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash for Balance Sheets and Cash Flows (Detail)

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Basis of Presentation - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash for Balance Sheets and Cash Flows (Detail) - USD ($)
$ in Millions
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Cash and cash equivalents $ 1,198.9 $ 1,278.8    
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows 1,215.0 1,295.5 $ 856.9 $ 904.4
Prepaid expenses and other current assets [Member]        
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Restricted cash 3.3 4.0    
Other Assets [Member]        
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Restricted cash $ 12.8 $ 12.7