Subsequent Events (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014 Building sqft		Feb. 24, 2014 sqft Building
Numberof Buildings Acquired [Roll Forward]
Number of Buildings	4,714
Square feet of property	113,800,000
Real Estate Investment, Aggregate Purchase Price	$ 19,854	[1]
Subsequent Event [Member]
Numberof Buildings Acquired [Roll Forward]
Number of Buildings			4,659
Square feet of property			103,200,000
Real Estate Investment, Aggregate Purchase Price			17,860	[1]
Property Acquisition [Member]
Numberof Buildings Acquired [Roll Forward]
Number of Buildings			(55)	[2]
Square feet of property			(10,600,000)	[2]
Real Estate Investment, Aggregate Purchase Price			$ (1,994)	[1],[2]

[1] Contract purchase price, excluding acquisition and transaction related costs.

[2] Includes the sale of the Multi-Tenant Portfolio, consisting of 71 properties.