Senior Unsecured Notes and Secured Debt (Details)	3 Months Ended		3 Months Ended								3 Months Ended
	Mar. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Mar. 31, 2015 Senior Unsecured Notes [Member] USD ($)		Mar. 31, 2015 Secured Debt [Member] USD ($)		Mar. 31, 2015 Canadian Denominated Unsecured Term Loan [Member] USD ($)	Mar. 31, 2015 Canadian Denominated Unsecured Term Loan [Member] CAD	Mar. 31, 2015 Canadian Denominated Unsecured Term Loan [Member] London Interbank Offered Rate (LIBOR) [Member]	Mar. 31, 2015 Unsecured Line of Credit Term Loan [Member] USD ($)	Mar. 31, 2015 UK Debt Due 2034 [Member] USD ($)	Mar. 31, 2015 UK Debt Due 2034 [Member] GBP (£)	Mar. 31, 2015 UK Debt Due 2028 [Member] USD ($)	Mar. 31, 2015 UK Debt Due 2028 [Member] GBP (£)	Mar. 31, 2015 Unsecured term credit facility [Member] USD ($)	Mar. 31, 2015 Unsecured term credit facility [Member] London Interbank Offered Rate (LIBOR) [Member]
Principal payments due on debt obligations
2015	$ 332,035,000		$ 0	[1],[2]	$ 332,035,000	[1],[3]
2016	1,193,223,000		700,000,000	[1],[2]	493,223,000	[1],[3]
2017	829,397,000		450,000,000	[1],[2]	379,397,000	[1],[3]
2018	894,394,000		450,000,000	[1],[2]	444,394,000	[1],[3]
2019	1,668,950,000		1,297,150,000	[1],[2],[4],[5]	371,800,000	[1],[3]
Thereafter	5,622,580,000		4,670,771,000	[1],[2],[6],[7]	951,809,000	[1],[3]
Totals	10,540,579,000		7,567,921,000	[1],[2]	2,972,658,000	[1],[3]
Senior Unsecured Notes and Secured Debt (Textual) [Abstract]
Notes, annual stated interest rates, Minimum			1.10%		1.00%
Notes, annual stated interest rates, Maximum			6.50%		7.90%
Interest rate											4.50%	4.50%	4.80%	4.80%
Senior unsecured notes issued amount											500,000,000	742,600,000	816,860,000	550,000,000
Senior unsecured notes	7,518,196,000	7,766,251,000					197,150,000	250,000,000		410,000,000					500,000,000
Secured debt	3,010,971,000	2,977,713,000
Carrying values of properties securing the debt					$ 5,349,988,000
Interest Rate margin	0.925%						2.00%	2.00%	0.975%						1.15%	0.975%
Debt Instrument, Issuance Date							Jul. 25, 2014	Jul. 25, 2014			Nov. 25, 2014	Nov. 25, 2014	Nov. 20, 2013	Nov. 20, 2013	Jul. 25, 2014
Debt instrument maturity date	Oct. 31, 2018						Oct. 31, 2018	Oct. 31, 2018			Nov. 24, 2034	Nov. 24, 2034	Nov. 20, 2028	Nov. 20, 2028	Oct. 31, 2018

[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 1.1% to 6.5%.

[3] (3) Annual interest rates range from 1.0% to 7.9%. Carrying value of the properties securing the debt totaled $5,349,988,000 at March 31, 2015.

[4] (5) On July 25, 2014, we refinanced the funding on a $500,000,000 unsecured term credit facility. The loan matures on October 31, 2018 (with an option to extend for one additional year at our discretion) and bears interest at LIBOR plus 97.5 basis points (1.15% at March 31, 2015).

[5] (4) On July 25, 2014, we refinanced the funding on a $250,000,000 Canadian-denominated unsecured term credit facility (approximately $197,150,000 based on the Canadian/U.S. Dollar exchange rate on March 31, 2015). The loan matures on October 31, 2018 (with an option to extend for an additional year at our discretion) and bears interest at the Canadian Dealer Offered Rate plus 97.5 basis points (2.0% at March 31, 2015).

[6] (6) On November 20, 2013, we completed the sale of £550,000,000 (approximately $816,860,000 based on the Sterling/U.S. Dollar exchange rate in effect on March 31, 2015) of 4.8% senior unsecured notes due 2028.

[7] (7) On November 25, 2014, we completed the sale of £500,000,000 (approximately $742,600,000 based on the Sterling/U.S. Dollar exchange rate in effect on March 31, 2015) of 4.5% senior unsecured notes due 2034.