Debt (Details)				9 Months Ended			0 Months Ended			0 Months Ended		9 Months Ended			0 Months Ended	1 Months Ended					1 Months Ended		1 Months Ended		9 Months Ended
	Sep. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Sep. 30, 2012 Line of Credit and Term Loan USD ($)	Sep. 30, 2012 Bank Line of Credit USD ($)	Sep. 30, 2012 Bank Line of Credit GBP (£)	Mar. 27, 2012 Bank Line of Credit USD ($)	Jul. 30, 2012 Term Loan USD ($)	Jul. 30, 2012 Term Loan GBP (£)	Sep. 30, 2012 Term Loan USD ($)	Jul. 30, 2012 Term Loan Interest-rate swap contracts	Jan. 24, 2011 Senior Unsecured Notes USD ($)	Sep. 30, 2012 Senior Unsecured Notes USD ($)	Sep. 30, 2012 Senior Unsecured Notes Minimum	Sep. 30, 2012 Senior Unsecured Notes Maximum	Jun. 25, 2012 Senior Unsecured, 6.45% notes due 2012 USD ($)	Sep. 30, 2011 Senior Unsecured, 4.82% notes due 2011 USD ($)	Jan. 24, 2011 Senior Unsecured, 2.70% notes due 2014 USD ($)	Jan. 24, 2011 Senior Unsecured, 3.75% notes due 2016 USD ($)	Jan. 24, 2011 Senior Unsecured, 5.375% notes due 2021 USD ($)	Jan. 24, 2011 Senior Unsecured, 6.75% notes due 2041 USD ($)	Jan. 31, 2012 Senior Unsecured, 3.75% notes due 2019 USD ($)	Jan. 23, 2012 Senior Unsecured, 3.75% notes due 2019 USD ($)	Jul. 31, 2012 Senior Unsecured, 3.15% notes due 2022 USD ($)	Jul. 23, 2012 Senior Unsecured, 3.15% notes due 2022 USD ($)	Sep. 30, 2012 Mortgage Debt USD ($) item	Sep. 30, 2012 Mortgage Debt Minimum	Sep. 30, 2012 Mortgage Debt Maximum	Sep. 30, 2012 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	1 year
Debt instrument, variable rate basis				LIBOR			GBP LIBOR	GBP LIBOR
Debt instrument, basis spread on variable rate (as a percent)				1.075%			1.20%	1.20%
Debt instrument, facility fee (as a percent)				0.175%
Line of credit facility additional aggregate amount				500,000,000
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			8,300,000,000
Debt instrument, effective interest rate (as a percent)																						3.83%		3.28%
Weighted-average interest rate (as a percent)											4.83%	5.40%													6.14%
Weighted-average maturity											10 years 3 months 18 days	6 years 1 month 10 days													3 years 9 months 18 days
Issuance of senior unsecured notes											2,400,000,000						400,000,000	500,000,000	1,200,000,000	300,000,000		450,000,000		300,000,000
Debt issuance price as a percentage of principal amount																						99.523%		98.888%
Net proceeds from issuance of senior unsecured notes											2,370,000,000										444,000,000		294,000,000
Repayment of senior unsecured notes															250,000,000	292,000,000
Stated interest rate (as a percent)													1.29%	7.07%	6.45%	4.82%	2.70%	3.75%	5.375%	6.75%		3.75%		3.15%		1.54%	8.69%
2012 (Three months)	8,715,000																								8,715,000
2013	870,207,000											550,000,000													320,207,000
2014	671,495,000											487,000,000													184,495,000
2015	704,761,000											400,000,000													304,761,000
2016	1,414,389,000								221,214,000			900,000,000													293,175,000
Thereafter	4,184,762,000											3,600,000,000													584,762,000
Debt instrument principal outstanding, total	7,854,329,000								221,214,000			5,937,000,000													1,696,115,000
(Discounts) and premiums, net	(34,911,000)											(23,310,000)													(11,601,000)
Debt instruments, carrying amount	7,819,418,000								221,214,000			5,913,690,000													1,684,514,000
Unsecured term loan	221,214,000						221,000,000	137,000,000
Maturity period of debt instruments							4 years	4 years
Term of the interest rate swap agreement										4 years
Debt instrument, fixed interest rate (as a percent)										1.81%
Bank line of credit		454,000,000		221,000,000	137,000,000
Senior unsecured notes	5,913,690,000	5,416,063,000
Mortgage debt	1,684,514,000	1,715,039,000																							1,700,000,000
Number of healthcare facilities used to secure debt																									137
Debt instrument, collateral, healthcare facilities carrying value																									2,100,000,000
Portion of other debt and occupancy fee deposits excluded from schedule of debt maturities	84,580,000	87,985,000																										85,000,000
Number of CCRC issuing life care bonds																												2
Non-interest bearing occupancy fee deposits																												2
Debt instrument, principal outstanding, refundable upon moving out																												28,000,000
Debt instrument, principal outstanding, refundable after remarketed																												$ 57,000,000