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Statement of Cash Flows - Summary of Non-cash Investing and Financing Activities (Details) - USD ($)
$ in Millions
9 Months Ended 12 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Dec. 31, 2020
Dec. 31, 2019
Cash and Cash Equivalents [Abstract]        
Accrued capital expenditures $ 70.1 $ 100.4 $ 83.6 $ 133.7