Reconciliation of Carrying Amounts of Real Estate Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings Per Share [Abstract]
Beginning Balance	$ 15,370	$ 15,546	$ 15,463
Additions:
Acquisitions		625	1,013
Capital expenditures and transfers from construction-in-progress	446	332	249
Deductions:
Dispositions and other	(174)	(1,127)	(551)
Impairments		(6)	(260)
Assets held for sale			(368)
Ending Balance	$ 15,642	$ 15,370	$ 15,546