Reconciliation of Carrying Amounts of Real Estate Investments (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Beginning Balance	$ 15,516	$ 15,160	$ 15,245
Additions:
Acquisitions	58	419	137
Capital expenditures and transfers from construction-in-progress	510	383	285
Deductions:
Dispositions and other	(331)	(368)	(501)
Impairments			(6)
Assets held for sale	(223)	(78)
Ending Balance	$ 15,530	$ 15,516	$ 15,160