Schedule III - Real Estate and Accumulated Depreciation (Summary - Investment in Real Estate and Accumulated Depreciation) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Investment in real estate:
Balance at beginning of year	$ 30,581,948	$ 30,041,058	$ 29,865,490
Acquisitions and development	4,598,670	1,276,636	2,834,279
Improvements	266,183	250,276	219,146
Deconsolidation of previously consolidated venture	0	(144,897)	0
Impairment of assets	(71,336)	(101,527)	(37,207)
Dispositions And other	(1,330,679)	(1,203,247)	(2,411,219)
Foreign currency translation	(454,398)	415,879	(429,431)
Other	0	47,770	0
Balance at end of year	33,590,388	30,581,948	30,041,058
Accumulated depreciation:
Balance at beginning of year	4,838,370	4,093,494	3,796,297
Depreciation and amortization expenses	950,459	921,720	901,242
Amortization of above market leases	6,375	7,303	7,909
Disposition and other	(205,562)	(192,029)	(514,651)
Foreign currency translation	(89,684)	7,882	(97,303)
Balance at end of year	5,499,958	$ 4,838,370	$ 4,093,494
Reconciliation of real property (Textual) [Abstract]
Aggregate cost for tax purposes for real property	$ 25,618,090