Dispositions of Real Estate and Discontinued Operations - Dispositions of Real Estate (Details)		1 Months Ended							3 Months Ended			6 Months Ended		12 Months Ended
	Jan. 31, 2020 property	Jun. 30, 2021 USD ($) property	May 31, 2021 USD ($) property	Apr. 30, 2021 USD ($) property	Mar. 31, 2021 USD ($) property	Feb. 28, 2021 USD ($) property	Jan. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Jun. 30, 2021 USD ($) property	Mar. 31, 2021 USD ($) property	Jun. 30, 2020 USD ($) property	Jun. 30, 2021 USD ($) property	Jun. 30, 2020 USD ($) property	Dec. 31, 2020 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided by financing activities												$ (2,009,272,000)	$ 867,584,000
Gain on sales of real estate, net									$ 175,238,000		$ 81,284,000	175,238,000	$ 83,353,000
Repayments of secured debt								$ 6,000,000
Number of properties disposed | property													18
Carrying value of mortgages assumed by buyer in real estate dispositions												$ 106,632,000	$ 0
Number of loans sold | property		2						3	2			2		3
Mortgage Debt
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets classified as discontinued operations | property			6	2	2			1		2				1
Repayments of secured debt				$ 64,000,000	$ 39,000,000
Disposal Group, Disposed of by Means Other than Sale, Not Discontinued Operations, Abandonment
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sales of real estate, net									$ 10,000,000		83,000,000		247,000,000	$ 283,000,000
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sales of real estate, net									7,000,000		2,000,000		164,000,000	$ 193,000,000
Brookedale MTCA
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sales of real estate, net							$ 164,000,000
Number of properties disposed | property	18													18
Sunrise Senior Housing Portfolio | SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net cash provided by financing activities							410,000,000
Capital expenditure funding, amount committed		$ 56,000,000					92,000,000
Capital expenditure funding, amount funded												$ 0
Oakmont SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Carrying value of mortgages assumed by buyer in real estate dispositions				$ 107,000,000
Oakmont SHOP Portfolio | Mortgage Debt
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property				4
Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property														21
Proceeds from sale of buildings									12,000,000				385,000,000	$ 428,000,000
Senior housing triple-net | Brookdale Triple Net Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings							510,000,000
Gain on sales of real estate, net							169,000,000
Senior housing triple-net | HRA Triple Net Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings						$ 132,000,000
Gain on sales of real estate, net						$ 33,000,000
Senior housing triple-net | Aegis NNN Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings								$ 358,000,000
Gain on sales of real estate, net								$ 228,000,000
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings							230,000,000		$ 44,000,000		$ 28,000,000		$ 64,000,000	190,000,000
Net cash provided by financing activities							150,000,000
Gain on sales of real estate, net							$ 59,000,000			$ (16,000,000)		$ 7,000,000
SHOP | Oakmont SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings				$ 564,000,000
Gain on sales of real estate, net				80,000,000
SHOP | Discovery SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings				334,000,000
Gain on sales of real estate, net				9,000,000
Proceeds from sale of loans and preferred equity method investments				21,000,000
SHOP | Sonata SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings				64,000,000
Gain on sales of real estate, net				$ 3,000,000
SHOP | Atria SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property								12
Proceeds from sale of buildings								$ 312,000,000
Gain on sales of real estate, net								$ 39,000,000
Medical office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings														136,000,000
MOB Land Parcels
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings														$ 3,000,000
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property							16		6		2	1	9	23
Proceeds from sale of buildings												$ 5,000,000
SHOP | Sunrise Senior Housing Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		2					32
Proceeds from sale of buildings							$ 664,000,000
Net cash provided by financing activities							$ 410,000,000
Gain on sales of real estate, net		$ (7,000,000)
SHOP | Oakmont SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property				12
SHOP | Discovery SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property				10
Gain on sales of real estate, net				$ 0
Number of preferred equity method investments sold | property				2
SHOP | Discovery SHOP Portfolio | Secured Loans
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of loans sold | property				2
SHOP | Sonata SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property				5
SHOP | SLC SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property			7
Repayments of secured debt			$ 70,000,000
SHOP | SLC SHOP Portfolio | Definitive Agreement Four
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings			113,000,000
Gain on sales of real estate, net			$ 1,000,000
SHOP | Atria SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property								4
Net cash provided by financing activities								$ 61,000,000
Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property									3				18
Senior housing triple-net | Sunrise Senior Housing Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		2
Proceeds from sale of buildings		$ 80,000,000
Gain on sales of real estate, net		$ 22,000,000
Senior housing triple-net | Brookdale Triple Net Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property							24
Senior housing triple-net | HRA Triple Net Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property						8
Senior housing triple-net | Aegis NNN Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property								10
Medical Office, Hospital
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property			1
Proceeds from sale of buildings			$ 226,000,000
Gain on sales of real estate, net			$ 172,000,000
Medical office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property									4		3		3	11
Proceeds from sale of buildings									$ 21,000,000		$ 106,000,000		$ 106,000,000
Medical office | San Diego
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property														3
MOB Land Parcels
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property														2
Other Non-reportable Segments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property														1
Proceeds from sale of buildings														$ 1,000,000