Reconciliation of Carrying Amounts of Real Estate Investments (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Real Estate And Accumulated Depreciation [Line Items]
Beginning Balance	$ 15,661	$ 15,020	$ 13,749
Additions:
Acquisitions	184	427	1,155
Capital expenditures and transfers from construction-in-progress	353	443	338
Deductions:
Dispositions and other	(789)	(172)	(214)
Impairments	(1)	(57)	(8)
Ending Balance	$ 15,408	$ 15,661	$ 15,020