Reconciliation of Carrying Amounts of Real Estate Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share [Abstract]
Beginning Balance	$ 15,326	$ 15,408	$ 15,661
Additions:
Acquisitions	419	137	184
Capital expenditures and transfers from construction-in-progress	391	288	353
Deductions:
Dispositions and other	(368)	(501)	(789)
Impairments		(6)	(1)
Ending Balance	15,690	$ 15,326	$ 15,408
Assets held for sale	$ (78)