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Basis of Presentation and Significant Accounting Policies (Details) - USD ($)
 3 Months Ended 9 Months Ended
Sep. 30, 2020
Jun. 30, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Mar. 31, 2020
Dec. 31, 2019
Jun. 30, 2019
Mar. 31, 2019
Dec. 31, 2018
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                    
Asset impairments $ 0 $ 18,600,000 $ 0 $ 18,600,000 $ 0          
Accounting Standards Update [Extensible List]       us-gaap:AccountingStandardsUpdate201613Member            
Reduction to opening retained earnings 1,919,800,000 1,818,300,000 1,858,600,000 $ 1,919,800,000 1,858,600,000 $ 1,850,100,000 $ 1,893,900,000 $ 1,815,600,000 $ 1,855,800,000 $ 1,831,600,000
Retained Earnings                    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                    
Reduction to opening retained earnings $ 1,846,600,000 $ 1,768,600,000 $ 1,711,400,000 $ 1,846,600,000 $ 1,711,400,000 $ 1,785,100,000 1,761,300,000 $ 1,669,700,000 $ 1,639,300,000 $ 1,606,100,000
Cumulative Effect, Period of Adoption, Adjustment                    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                    
Reduction to opening retained earnings             (11,100,000)      
Cumulative Effect, Period of Adoption, Adjustment | Retained Earnings                    
New Accounting Pronouncements or Change in Accounting Principle [Line Items]                    
Reduction to opening retained earnings             $ (11,100,000)