Debt (Details)			6 Months Ended			1 Months Ended		1 Months Ended		1 Months Ended					1 Months Ended		1 Months Ended					1 Months Ended		1 Months Ended
	Jun. 30, 2012 USD ($)	Dec. 31, 2011 USD ($)	Jun. 30, 2012 Bank Line of Credit USD ($)	Jun. 30, 2012 Bank Line of Credit GBP (£)	Mar. 27, 2012 Bank Line of Credit USD ($)	Jul. 31, 2012 Unsecured term loan Y	Jul. 30, 2012 Unsecured term loan GBP (£)	Jul. 31, 2012 Unsecured term loan Interest-rate swap contracts	Jul. 30, 2012 Unsecured term loan Interest-rate swap contracts	Jan. 31, 2011 Senior Unsecured Notes USD ($)	Jun. 30, 2012 Senior Unsecured Notes USD ($) Y	Jan. 24, 2011 Senior Unsecured Notes USD ($) Y	Jun. 30, 2012 Senior Unsecured Notes Minimum	Jun. 30, 2012 Senior Unsecured Notes Maximum	Jun. 30, 2012 Senior Unsecured, 6.45% notes due 2012 USD ($)	Jun. 25, 2012 Senior Unsecured, 6.45% notes due 2012	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 ($)	Jun. 30, 2012 Mortgage Debt USD ($) Y item	Jun. 30, 2012 Mortgage Debt Minimum	Jun. 30, 2012 Mortgage Debt Maximum	Jun. 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
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			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)																									3.28%	6.14%
Weighted-average interest rate (as a percent)			2.07%								5.51%	4.83%
Weighted-average maturity (in years)											6.17	10.3														3.93
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																									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)													1.37%	7.07%		6.45%	4.82%	2.70%	3.75%	5.375%	6.75%		3.75%		3.15%		1.54%	8.72%
2012 (Six months)	28,148,000																									28,148,000
2013	917,374,000										550,000,000															367,374,000
2014	670,758,000										487,000,000															183,758,000
2015	702,102,000										400,000,000															302,102,000
2016	1,400,601,000		215,015,000								900,000,000															285,586,000
Thereafter	3,872,687,000										3,300,000,000															572,687,000
Debt instrument principal outstanding, total	7,591,670,000										5,637,000,000															1,739,655,000
(Discounts) and premiums, net	(33,732,000)										(21,021,000)															(12,711,000)
Debt instruments, carrying amount	7,557,938,000
Unsecured term loan							137,000,000
Maturity period of debt instruments (in years)						4
Maturity terms of agreements								4 years
Debt instrument, fixes interest rate (as a percent)									1.81%
Bank line of credit	215,015,000	454,000,000	215,015,000	137,000,000
Senior unsecured notes	5,615,979,000	5,416,063,000									5,615,979,000
Mortgage debt	1,726,944,000	1,764,571,000																								1,726,944,000
Number of healthcare facilities used to secure debt																										135
Debt instrument, collateral, healthcare facilities carrying value																										2,200,000,000
Portion of other debt and occupancy fee deposits excluded from schedule of debt maturities	84,060,000	87,985,000																											84,000,000
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																													$ 56,000,000