Shareholders' Equity/Partners' Capital (Schedule of Dividends) (Details) - $ / shares	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020	Dec. 31, 2020
Class of Stock [Line Items]
Common shares, dividends (in dollars per share)	$ 0.53	$ 0.66	$ 1.06	$ 1.32
Common shares of beneficial interest: authorized shares (shares)	250,000,000		250,000,000		250,000,000
Preferred shares of beneficial interest: authorized shares (shares)	110,000,000		110,000,000		110,000,000
Common Class A
Class of Stock [Line Items]
Common shares of beneficial interest: authorized shares (shares)	250,000,000	250,000,000	250,000,000	250,000,000
Convertible Preferred Stock | Common Class A
Class of Stock [Line Items]
Common shares, dividends (in dollars per share)	$ 0.53	$ 0.66	$ 1.06	$ 1.32
Convertible Preferred Stock | Series A Preferred Stock
Class of Stock [Line Items]
Common shares, dividends (in dollars per share)	0.53	0.66	1.06	1.32
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 0.8125	$ 0.8125	$ 1.6250	$ 1.6250
Preferred stock, dividend rate, percentage (percent)	6.50%	6.50%	6.50%	6.50%
Preferred shares of beneficial interest: authorized shares (shares)	13,402	13,694	13,402	13,694
Preferred stock, redemption price per share (in dollars per share/unit)	$ 1.9531	$ 1.9531	$ 1.9531	$ 1.9531
Redeemable Preferred Stock | Series K Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 0.3563	$ 0.3563	$ 0.7126	$ 0.7126
Preferred stock, dividend rate, percentage (percent)	5.70%	5.70%	5.70%	5.70%
Preferred shares of beneficial interest: authorized shares (shares)	12,000,000	12,000,000	12,000,000	12,000,000
Preferred stock, liquidation preference per share (in dollars per share/unit)	$ 25.00		$ 25.00
Redeemable Preferred Stock | Series L Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 0.3375	$ 0.3375	$ 0.6750	$ 0.6750
Preferred stock, dividend rate, percentage (percent)	5.40%	5.40%	5.40%	5.40%
Preferred shares of beneficial interest: authorized shares (shares)	13,800,000,000	13,800,000,000	13,800,000,000	13,800,000,000
Preferred stock, liquidation preference per share (in dollars per share/unit)		$ 25.00		$ 25.00
Redeemable Preferred Stock | Series M Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 0.3281	$ 0.3281	$ 0.6562	$ 0.6562
Preferred stock, dividend rate, percentage (percent)	5.25%	5.25%	5.25%	5.25%
Preferred shares of beneficial interest: authorized shares (shares)	13,800,000	13,800,000	13,800,000	13,800,000
Redeemable Preferred Stock | Series N Preferred Stock
Class of Stock [Line Items]
Preferred stock, dividend rate, per-dollar-amount (in dollars per share)	$ 0.3281		$ 0.6562
Preferred stock, dividend rate, percentage (percent)	5.25%		5.25%
Preferred shares of beneficial interest: authorized shares (shares)	12,000,000,000		12,000,000,000
Class A Unit | Convertible Preferred Stock | Series A Preferred Stock
Class of Stock [Line Items]
Preferred stock, redemption price per share (in dollars per share/unit)	$ 1.9531	$ 1.9531	$ 1.9531	$ 1.9531