Debt (Details)				0 Months Ended	12 Months Ended	0 Months Ended		0 Months Ended		12 Months Ended														0 Months Ended						0 Months Ended			12 Months Ended
	Dec. 31, 2012 USD ($) item	Dec. 31, 2011 USD ($)	Dec. 31, 2012 Line of Credit and Term Loan USD ($)	Mar. 27, 2012 Bank Line of Credit USD ($)	Dec. 31, 2012 Bank Line of Credit	Jul. 30, 2012 2012 Term Loan GBP (£)	Dec. 31, 2012 2012 Term Loan USD ($)	Jul. 30, 2012 2012 Term Loan Interest-rate swap contracts	Jan. 24, 2011 Senior Unsecured Notes USD ($)	Dec. 31, 2012 Senior Unsecured Notes USD ($)	Dec. 31, 2012 Senior Unsecured Notes Minimum	Dec. 31, 2012 Senior Unsecured Notes Maximum	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2013 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2014 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2015 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2016 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2017 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2018 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2019 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2020 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2021 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2022 USD ($)	Dec. 31, 2012 Senior Unsecured Notes Debt instrument maturing in 2041 USD ($)	Jun. 25, 2012 Senior Unsecured, 6.45% notes due 2012 USD ($)	Sep. 15, 2011 Senior Unsecured, 4.82% notes due 2011 USD ($)	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. 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 ($)	Dec. 31, 2012 Mortgage Debt USD ($) item	Dec. 31, 2012 Mortgage Debt Minimum	Dec. 31, 2012 Mortgage Debt Maximum	Dec. 31, 2012 Mortgage Debt Debt instrument maturing in 2013 USD ($)	Dec. 31, 2012 Mortgage Debt Debt instrument maturing in 2014 USD ($)	Dec. 31, 2012 Mortgage Debt Debt instrument maturing in 2015 USD ($)	Dec. 31, 2012 Mortgage Debt Debt instrument maturing in 2016 USD ($)	Dec. 31, 2012 Mortgage Debt Debt instrument maturing in 2017 USD ($)	Dec. 31, 2012 Mortgage Debt Thereafter USD ($)	Dec. 31, 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, maximum				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			9,200,000,000
Debt instrument, effective interest rate (as a percent)																														3.83%	3.28%	2.667%
Weighted-average interest rate (as a percent)									4.83%	5.10%			5.80%	3.15%	6.64%	5.07%	6.04%	6.83%	3.96%	2.79%	5.53%	3.39%	6.89%										6.13%			6.15%	5.78%	6.03%	6.88%	6.04%	5.26%
Weighted-average maturity									10 years 3 months 18 days	6 years																							4 years
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	800,000,000
Debt issuance price as a percentage of principal amount																														99.523%	98.888%	99.729%
Net proceeds from issuance of senior unsecured notes									2,370,000,000																					444,000,000	294,000,000	793,000,000
Repayment of senior unsecured notes																								250,000,000	292,000,000
Stated interest rate (as a percent)											1.21%	7.07%												6.45%	4.82%	2.70%	3.75%	5.375%	6.75%	3.75%	3.15%	2.625%		1.54%	8.69%
2013	841,747,000									550,000,000																							291,747,000
2014	666,695,000									487,000,000																							179,695,000
2015	708,048,000									400,000,000																							308,048,000
2016	1,414,032,000						222,694,000			900,000,000																							291,338,000
2017	1,300,052,000									750,000,000																							550,052,000
Thereafter	3,715,886,000									3,650,000,000																							65,886,000
Debt instrument principal outstanding, total	8,646,460,000						222,694,000			6,737,000,000			550,000,000	487,000,000	400,000,000	900,000,000	750,000,000	600,000,000	450,000,000	800,000,000	1,200,000,000	300,000,000	300,000,000										1,686,766,000			291,747,000	179,695,000	308,048,000	291,338,000	550,052,000	65,886,000
(Discounts) and premiums, net	(34,598,000)									(24,376,000)																							(10,222,000)
Debt instruments, carrying amount	8,611,862,000						222,694,000			6,712,624,000																							1,676,544,000
Unsecured term loan	222,694,000					137,000,000	223,000,000
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%
Bank line of credit		454,000,000
Senior unsecured notes	6,712,624,000	5,416,063,000								6,700,000,000
Mortgage debt	1,676,544,000	1,715,039,000																															1,700,000,000
Number of healthcare facilities used to secure debt																																	135
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	$ 81,958,000	$ 87,985,000																																								$ 82,000,000
Number of CCRC issuing life care bonds	2																																									2
Non-interest bearing occupancy fee deposits																																										2