Debt (Details)				9 Months Ended	0 Months Ended			0 Months Ended	9 Months Ended			0 Months Ended					9 Months Ended
	Sep. 30, 2013 USD ($)	Dec. 31, 2012 USD ($)	Sep. 30, 2013 Line of Credit and Term Loan USD ($)	Sep. 30, 2013 Bank Line of Credit USD ($)	Jul. 30, 2012 2012 Term Loan GBP (£)	Sep. 30, 2013 2012 Term Loan USD ($)	Sep. 30, 2013 2012 Term Loan GBP (£)	Jul. 30, 2012 2012 Term Loan Interest-rate swap contracts	Sep. 30, 2013 Senior Unsecured Notes USD ($)	Sep. 30, 2013 Senior Unsecured Notes Minimum	Sep. 30, 2013 Senior Unsecured Notes Maximum	Jun. 25, 2012 Senior Unsecured, 6.45% notes due 2012 USD ($)	Jan. 23, 2012 Senior Unsecured, 3.75% notes due 2019 USD ($)	Jul. 23, 2012 Senior Unsecured, 3.15% notes due 2022 USD ($)	Nov. 19, 2012 Senior Unsecured, 2.625% notes due 2020 USD ($)	Feb. 28, 2013 Senior Unsecured, 5.625% USD ($)	Sep. 30, 2013 Mortgage Debt USD ($) item	Sep. 30, 2013 Mortgage Debt Minimum	Sep. 30, 2013 Mortgage Debt Maximum	Sep. 30, 2013 Other Debt USD ($) item
Debt Instrument
Line of credit facility, maximum borrowing capacity				$ 1,500,000,000
Length of debt instrument extension period				1 year	1 year
Debt instrument, variable rate basis				LIBOR	GBP LIBOR
Debt instrument, basis spread on variable rate (as a percent)				1.075%	1.20%
Debt instrument, facility fee (as a percent)				0.175%
Line of credit facility additional aggregate amount, maximum				500,000,000
Line of credit facility, amount outstanding				285,000,000
Debt instrument, covenant debt to assets (as a percent)			60.00%
Debt instrument, covenant secured debt to assets (as a percent)			30.00%
Debt instrument, covenant unsecured debt to unencumbered assets (as a percent)			60.00%
Debt instrument, covenant minimum fixed charge coverage ratio			1.5
Debt instrument, covenant net worth			9,200,000,000
Debt instrument, effective interest rate (as a percent)													3.80%	3.30%	2.70%
Weighted-average interest rate (as a percent)									5.10%								6.16%
Weighted-average maturity									5 years								4 years
Issuance of senior unsecured notes													450,000,000	300,000,000	800,000,000
Debt issuance price as a percentage of principal amount													99.50%	98.90%	99.70%
Net proceeds from issuance of senior unsecured notes													444,000,000	294,000,000	793,000,000
Repayment of senior unsecured notes												250,000,000				150,000,000
Stated interest rate (as a percent)										1.22%	6.98%	6.45%	3.75%	3.15%	2.625%	5.625%		0.69%	8.69%
2013 (Three months)	414,003,000								400,000,000								14,003,000
2014	667,042,000								487,000,000								180,042,000
2015	708,421,000								400,000,000								308,421,000
2016	1,698,486,000			285,000,000		221,748,000			900,000,000								291,738,000
2017	1,300,477,000								750,000,000								550,477,000
Thereafter	3,721,825,000								3,650,000,000								71,825,000
Debt instrument principal outstanding, total	8,510,254,000			285,000,000		221,748,000			6,587,000,000								1,416,506,000
(Discounts) and premiums, net	(27,165,000)								(21,066,000)								(6,099,000)
Debt instruments, carrying amount	8,483,089,000			285,000,000	137,000,000	222,000,000	137,000,000		6,565,934,000								1,410,407,000
Maturity period of debt instruments					4 years
Term of the interest rate swap agreement								4 years
Debt instrument, fixed interest rate (as a percent)								1.81%
Number of healthcare facilities used to secure debt																	132
Debt instrument, collateral, healthcare facilities carrying value																	2,000,000,000
Portion of other debt and occupancy fee deposits excluded from schedule of debt maturities	$ 77,503,000	$ 81,958,000																		$ 78,000,000
Number of continuing care retirement communities issuing life care bonds																				2
Non-interest bearing occupancy fee deposits																				2