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Cumulative Preferred Stock (Characteristics of the First Preferred Shares) (Details) - $ / shares |  |  | 12 Months Ended
--- | --- | --- | ---
Aug. 15, 2020 | Jul. 16, 2020 | Dec. 31, 2020 | Dec. 31, 2019
Series A Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  | 2.182% | 4.40% |
Current Annual Dividend | $ 0.5456 |  | $ 0.6388 |
Earliest Redemption and/or Conversion Option Date |  |  | Aug. 15, 2025 |
Redemption Value |  |  | $ 25 |
Preferred Stock, Conversion Basis |  |  | Right to Convert on a one for one basis |
Conversion of Stock, Type of Stock Converted |  |  | Series B |
Series A Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 1.84% |
Series A Preferred Stock | Maximum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Redemption Value |  |  | $ 25 |
Series C Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 4.10% |
Current Annual Dividend | 1.1802 |  | $ 1.1802 | $ 1.0505
Earliest Redemption and/or Conversion Option Date |  |  | Aug. 15, 2023 |
Redemption Value |  |  | $ 25 |
Preferred Stock, Conversion Basis |  |  | Right to Convert on a one for one basis |
Conversion of Stock, Type of Stock Converted |  |  | Series D |
Series C Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 2.65% |
Series C Preferred Stock | Maximum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Redemption Value |  |  | $ 25 |
Series F Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 4.202% |
Current Annual Dividend | $ 1.0505 |  | $ 1.0625 |
Earliest Redemption and/or Conversion Option Date |  |  | Feb. 15, 2025 |
Redemption Value |  |  | $ 25 |
Preferred Stock, Conversion Basis |  |  | Right to Convert on a one for one basis |
Conversion of Stock, Type of Stock Converted |  |  | Series G |
Right to Convert on a one for one basis |  |  | The holders of the Series F Shares have the right, at their option, to convert all or any of their Series F Shares, on a one-for-one basis, into Cumulative Floating Rate First Preferred Shares, Series G of the Company on February 15, 2020, or to continue to hold their Series F Shares. |
Series F Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 2.63% |
Series F Preferred Stock | Maximum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Redemption Value |  |  | $ 25 |
Series B Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  | 2.021% | 2.393% |
Earliest Redemption and/or Conversion Option Date |  |  | Aug. 15, 2025 |
Redemption Value |  |  | $ 25 |
Preferred Stock, Conversion Basis |  |  | Right to Convert on a one for one basis |
Conversion of Stock, Type of Stock Converted |  |  | Series A |
Series B Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 1.84% |
Series H Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 4.90% |
Current Annual Dividend |  |  | $ 1.225 |
Earliest Redemption and/or Conversion Option Date |  |  | Aug. 15, 2023 |
Redemption Value |  |  | $ 25 |
Preferred Stock, Conversion Basis |  |  | Right to Convert on a one for one basis |
Conversion of Stock, Type of Stock Converted |  |  | Series I |
Series H Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 4.90% |
Series H Preferred Stock | Maximum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Redemption Value |  |  | $ 25 |
Series I Preferred Stock | Minimum |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 2.54% |
Perpetual fixed rate Series E Preferred Stock |  |  |  |
Class of Stock [Line Items] |  |  |  |
Initial Yield |  |  | 4.50% |
Current Annual Dividend |  |  | $ 1.125 |
Redemption Value |  |  | $ 25.75 |

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