Quarterly report pursuant to Section 13 or 15(d)

Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash for Balance Sheets and Cash Flows (Detail)

v3.19.1
Significant Accounting Policies - Summary of Reconciliation of Cash, Cash Equivalents and Restricted Cash for Balance Sheets and Cash Flows (Detail) - USD ($)
$ in Millions
Mar. 31, 2019
Dec. 31, 2018
Mar. 31, 2018
Dec. 31, 2017
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Cash and cash equivalents $ 1,209.0 $ 1,198.9    
Total cash, cash equivalents, and restricted cash shown in the statement of cash flows 1,219.0 1,215.0 $ 1,347.0 $ 1,295.5
Prepaid expenses and other current assets [Member]        
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Restricted cash 2.2 3.3    
Other Assets [Member]        
Cash, Cash Equivalents and Restricted Cash [Line Items]        
Restricted cash $ 7.8 $ 12.8