Background Schedule of rentable square feet (Details)	Dec. 31, 2015 ft²
Real Estate Properties [Line Items]
Area of Real Estate Property	20,073,784
Square Footage of Real Estate Property, Future Development	11,965,247
Square Footage of Real Estate Property, Near-term and Future Development	11,900,000
Total Rentable Square Footage of Asset Base	32,039,031
Operating properties
Real Estate Properties [Line Items]
Area of Real Estate Property	16,737,994
Development
Real Estate Properties [Line Items]
Area of Real Estate Property	2,761,428
Redevelopment
Real Estate Properties [Line Items]
Area of Real Estate Property	574,362
North America | Future value-creation projects
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	5,545,540
Asia | Future value-creation projects
Real Estate Properties [Line Items]
Square Footage of Real Estate Property, Future Development	6,419,707