Indebtedness and Derivative Financial Instruments (Details)			0 Months Ended	12 Months Ended		12 Months Ended		12 Months Ended					12 Months Ended		12 Months Ended			12 Months Ended
	Dec. 31, 2013 USD ($)	Dec. 31, 2012 USD ($)	Jan. 02, 2014 Secured Debt Mortgages USD ($)	Dec. 31, 2013 Secured Debt Mortgages USD ($) note mortgagepool property	Dec. 31, 2012 Secured Debt Mortgages USD ($)	Dec. 31, 2013 Unsecured Debt Senior unsecured notes USD ($)	Dec. 31, 2012 Unsecured Debt Senior unsecured notes USD ($)	Dec. 31, 2013 Unsecured Debt Senior unsecured notes 5.30% to 7.18% USD ($)	Oct. 02, 2013 Unsecured Debt Senior unsecured notes 2.375% due October 2020 Operating Partnership USD ($)	Oct. 02, 2013 Unsecured Debt Senior unsecured notes 2.375% due October 2020 Operating Partnership EUR (€)	Jan. 21, 2014 Unsecured Debt Senior unsecured notes 2.20% due February 2019 Operating Partnership USD ($)	Jan. 21, 2014 Unsecured Debt Senior unsecured notes 3.75% due February 2024 Operating Partnership USD ($)	Dec. 31, 2013 Unsecured Debt Credit Facility and the Supplemental Facility USD ($) Item	Dec. 31, 2012 Unsecured Debt Credit Facility and the Supplemental Facility USD ($)	Dec. 31, 2013 Unsecured Debt Credit Facility USD ($)	Dec. 30, 2013 Unsecured Debt Credit Facility USD ($)	Dec. 31, 2013 Unsecured Debt Credit Facility Euro USD ($)	Dec. 31, 2013 Unsecured Debt Supplemental Facility USD ($)	Dec. 31, 2013 Unsecured Debt Term loan USD ($) Item
Fixed-Rate Debt:
Fixed-rate mortgages and other indebtedness	$ 21,826,232,000	$ 21,077,358,000		$ 7,894,527,000	$ 7,677,204,000	$ 13,931,705,000	$ 13,400,154,000
Weighted-average interest rate, fixed-rate debt (as a percent)				5.62%		4.87%
Net premiums				63,968,000	101,104,000
Net discount						38,519,000	38,847,000
Weighted average maturity period, fixed-rate debt				4 years 2 months 12 days		6 years 4 months 24 days
Variable-Rate Debt:
Variable-rate mortgages and other indebtedness	1,762,299,000	2,035,649,000		350,000,000	442,152,000
Credit facility, amount outstanding													1,172,299,000	1,593,497,000	960,100,000			212,200,000
Weighted average interest rate, variable-rate debt (as a percent)				1.52%
Weighted average maturity period, variable-rate debt				3 years 8 months 12 days
Total mortgages and other indebtedness	23,588,531,000	23,113,007,000		8,200,000,000	8,000,000,000	13,900,000,000											660,100,000		240,000,000
Number of non-recourse mortgage notes under which the Company and subsidiaries are borrowers				80
Number of properties secured by non-recourse mortgage notes				80
Number of cross-defaulted and cross-collateralized mortgage pools				7
Total number of properties pledged as collateral for cross defaulted and cross collateralized mortgages				27
Maximum borrowing capacity															4,000,000,000			2,000,000,000	300,000,000
Available borrowing capacity													4,800,000,000
Maximum amount outstanding during period													1,600,000,000
Credit facility, weighted average amount outstanding													1,300,000,000
Letters of credit outstanding													41,900,000
Number of credit facilities													2
Optional expanded maximum borrowing capacity															5,000,000,000			2,500,000,000
Reference rate															LIBOR			LIBOR	LIBOR
Interest added to reference rate (as a percent)															0.95%			0.95%	1.10%
Additional facility fee (as a percent)															0.15%			0.15%
Reduction in interest added to reference rate (as a percent)															0.05%			0.05%
Multi-currency tranche															2,000,000,000
Amount of debt redeemed				240,000,000				504,500,000
Interest rate, low end of range (as a percent)								5.30%
Interest rate, high end of range (as a percent)								7.18%
Number of one-year extension options available																			2
Debt instrument extension period																			1 year
Debt issued				370,000,000					1,000,000,000	750,000,000	600,000,000	600,000,000				300,000,000
Interest rate on debt (as a percent)									2.375%	2.375%	2.20%	3.75%
Average interest rate (as a percent)				4.04%
Debt repaid			$ 820,000,000