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Common Stock and Related Matters - Dividends Declared And Or Paid (Details) - USD ($)
$ / shares in Units, $ in Millions
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Dividends Payable [Line Items]      
Accrued preferred dividends payable date Feb. 12, 2021    
Dividends Declared per Share of Common Stock $ 1.21 $ 3.64 $ 3.64
Dividend Declared, Q4 2020 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date Feb. 16, 2021    
Total Common Dividends Declared $ 23.3    
Amount of Common Dividends Paid or To Be Paid 22.9    
Accrued Dividends [1] $ 0.4    
Dividends Declared per Share of Common Stock $ 0.10000    
Dividend Declared, Q3 2020 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date Nov. 16, 2020    
Total Common Dividends Declared $ 23.8    
Amount of Common Dividends Paid or To Be Paid 23.3    
Accrued Dividends [1] $ 0.5    
Dividends Declared per Share of Common Stock $ 0.10000    
Dividend Declared, Q2 2020 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date Aug. 17, 2020    
Total Common Dividends Declared $ 23.7    
Amount of Common Dividends Paid or To Be Paid 23.3    
Accrued Dividends [1] $ 0.4    
Dividends Declared per Share of Common Stock $ 0.10000    
Dividend Declared, Q1 2020 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date May 15, 2020    
Total Common Dividends Declared $ 23.7    
Amount of Common Dividends Paid or To Be Paid 23.3    
Accrued Dividends [1] $ 0.4    
Dividends Declared per Share of Common Stock $ 0.10000    
Dividend Declared, Q4 2019 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date   Feb. 18, 2020  
Total Common Dividends Declared   $ 216.0  
Amount of Common Dividends Paid or To Be Paid   212.0  
Accrued Dividends [1]   $ 4.0  
Dividends Declared per Share of Common Stock   $ 0.91000  
Dividend Declared, Q3 2019 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date   Nov. 15, 2019  
Total Common Dividends Declared   $ 215.5  
Amount of Common Dividends Paid or To Be Paid   211.8  
Accrued Dividends [1]   $ 3.7  
Dividends Declared per Share of Common Stock   $ 0.91000  
Dividend Declared, Q2 2019 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date   Aug. 15, 2019  
Total Common Dividends Declared   $ 215.1  
Amount of Common Dividends Paid or To Be Paid   211.5  
Accrued Dividends [1]   $ 3.6  
Dividends Declared per Share of Common Stock   $ 0.91000  
Dividend Declared, Q1 2019 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date   May 15, 2019  
Total Common Dividends Declared   $ 215.2  
Amount of Common Dividends Paid or To Be Paid   211.5  
Accrued Dividends [1]   $ 3.7  
Dividends Declared per Share of Common Stock   $ 0.91000  
Dividend Declared, Q4 2018 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date     Feb. 15, 2019
Total Common Dividends Declared     $ 215.2
Amount of Common Dividends Paid or To Be Paid     211.2
Accrued Dividends [1]     $ 4.0
Dividends Declared per Share of Common Stock     $ 0.91000
Dividend Declared, Q3 2018 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date     Nov. 15, 2018
Total Common Dividends Declared     $ 212.5
Amount of Common Dividends Paid or To Be Paid     208.6
Accrued Dividends [1]     $ 3.9
Dividends Declared per Share of Common Stock     $ 0.91000
Dividend Declared, Q2 2018 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date     Aug. 15, 2018
Total Common Dividends Declared     $ 208.9
Amount of Common Dividends Paid or To Be Paid     205.2
Accrued Dividends [1]     $ 3.7
Dividends Declared per Share of Common Stock     $ 0.91000
Dividend Declared, Q1 2018 [Member]      
Dividends Payable [Line Items]      
Accrued preferred dividends payable date     May 16, 2018
Total Common Dividends Declared     $ 203.1
Amount of Common Dividends Paid or To Be Paid     199.7
Accrued Dividends [1]     $ 3.4
Dividends Declared per Share of Common Stock     $ 0.91000
[1] Represents accrued dividends on restricted stock and restricted stock units that are payable upon vesting.