Senior Unsecured Notes and Secured Debt (Details)	1 Months Ended	6 Months Ended		3 Months Ended
	Jul. 25, 2014	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Jun. 30, 2014 Senior Unsecured Notes [Member] USD ($)		Jun. 30, 2014 Secured Debt [Member] USD ($)		Jun. 30, 2014 Canadian Denominated Unsecured Term Loan [Member] USD ($)	Jun. 30, 2014 Canadian Denominated Unsecured Term Loan [Member] CAD	Jun. 30, 2014 Unsecured Line of Credit Term Loan [Member] USD ($)	Jun. 30, 2014 UKDebt [Member] USD ($)	Jun. 30, 2014 UKDebt [Member] GBP (£)
Principal payments due on debt obligations
2014		$ 117,263,000		$ 0	[1],[2]	$ 117,263,000	[1],[3]
2015		893,733,000		484,170,000	[1],[2],[4]	409,563,000	[1],[3]
2016		1,572,528,000		1,200,000,000	[1],[2],[5]	372,528,000	[1],[3]
2017		777,347,000		450,000,000	[1],[2]	327,347,000	[1],[3]
2018		880,379,000		450,000,000	[1],[2]	430,379,000	[1],[3]
Thereafter		6,021,083,000		4,865,937,000	[1],[2],[6]	1,155,146,000	[1],[3]
Totals		10,262,333,000		7,450,107,000	[1],[2]	2,812,226,000	[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%
Interest rate								2.70%	2.70%	1.50%	4.80%	4.80%
Senior unsecured notes issued amount											940,830,000	550,000,000
Senior unsecured notes		7,411,243,000	7,379,308,000					234,170,000	250,000,000	500,000,000
Secured debt		2,850,103,000	3,058,248,000
Carrying values of properties securing the debt						$ 5,123,888,000
Interest Rate margin	1.05%	1.175%						1.45%	1.45%	1.35%
Debt instrument maturity date	Oct. 31, 2018	Mar. 31, 2017						Jul. 27, 2015	Jul. 27, 2015	Mar. 31, 2016
Loan Extension Period				2 years 0 months

[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 1.5% to 6.5%.

[3] (3) Annual interest rates range from 1.0% to 8.0%. Carrying value of the properties securing the debt totaled $5,123,888,000 at June 30, 2014.

[4] (4) On July 30, 2012, we completed funding on a $250,000,000 Canadian denominated unsecured term loan (approximately $234,170,000 based on the Canadian/U.S. Dollar exchange rate in effect on June 30, 2014). The loan matures on July 27, 2015 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 145 basis points (2.7% at June 30, 2014). Please see Note 19 for subsequent activity.

[5] (5) On January 8, 2013, we completed funding on a $500,000,000 unsecured term loan. The loan matures on March 31, 2016 (with an option to extend for two additional years at our discretion) and bears interest at LIBOR plus 135 basis points (1.5% at June 30, 2014). Please see Note 19 for subsequent activity.

[6] (6) On November 20, 2013, we completed the sale of £550,000,000 (approximately $940,830,000 based on the Sterling/U.S. Dollar exchange rate in effect on June 30, 2014) of 4.8% senior unsecured notes due 2028.