Senior Unsecured Notes and Secured Debt (Details)	9 Months Ended		3 Months Ended
	Sep. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Sep. 30, 2014 Senior Unsecured Notes [Member] USD ($)		Sep. 30, 2014 Secured Debt [Member] USD ($)		Sep. 30, 2014 Canadian Denominated Unsecured Term Loan [Member] USD ($)	Sep. 30, 2014 Canadian Denominated Unsecured Term Loan [Member] CAD	Sep. 30, 2014 Unsecured Line of Credit Term Loan [Member] USD ($)	Sep. 30, 2014 UKDebt [Member] USD ($)	Sep. 30, 2014 UKDebt [Member] GBP (£)
Principal payments due on debt obligations
2014	$ 50,367,000		$ 0	[1],[2]	$ 50,367,000	[1],[3]
2015	657,611,000		250,000,000	[1],[2],[4]	407,611,000	[1],[3]
2016	1,095,659,000		700,000,000	[1],[2],[5]	395,659,000	[1],[3]
2017	803,801,000		450,000,000	[1],[2]	353,801,000	[1],[3]
2018	1,605,264,000		1,173,055,000	[1],[2]	432,209,000	[1],[3]
Thereafter	5,991,346,000		4,769,273,000	[1],[2],[6]	1,222,073,000	[1],[3]
Totals	10,204,048,000		7,342,328,000	[1],[2]	2,861,720,000	[1],[3]
Senior Unsecured Notes and Secured Debt (Textual) [Abstract]
Notes, annual stated interest rates, Minimum			1.50%		1.00%
Notes, annual stated interest rates, Maximum			6.50%		8.00%
Senior unsecured notes issued amount										891,825,000	550,000,000
Senior unsecured notes	7,305,414,000	7,379,308,000					223,055,000	250,000,000	500,000,000
Secured debt	2,893,814,000	3,058,248,000
Carrying values of properties securing the debt					$ 5,121,039,000
Interest Rate margin	1.05%

[1] (1) Amounts represent principal amounts due and do not include unamortized premiums/discounts or other fair value adjustments as reflected on the balance sheet.

[2] (2) Annual interest rates range from 1.3% to 6.5%.

[3] (3) Annual interest rates range from 1.0% to 8.0%. Carrying value of the properties securing the debt totaled $5,121,039,000 at September 30, 2014.

[4] (4) On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $223,055,000 based on the Canadian/U.S. Dollar exchange rate in effect on September 30, 2014). This loan was refinanced on July 25, 2014. See Note 9 for additional information.

[5] (5) On January 8, 2013, we completed funding on a $500,000,000 unsecured term loan. This loan was refinanced on July 25, 2014. See Note 9 for additional information.

[6] (6) On November 20, 2013, we completed the sale of £550,000,000 (approximately $891,825,000 based on the Sterling/U.S. Dollar exchange rate in effect on September 30, 2014) of 4.8% senior unsecured notes due 2028.