Dispositions of Real Estate and Discontinued Operations - Dispositions of Real Estate (Details)		1 Months Ended					3 Months Ended		9 Months Ended	12 Months Ended
	Jan. 31, 2020 USD ($) property	Apr. 30, 2021 USD ($) property	Feb. 28, 2021 USD ($) property	Jan. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Oct. 31, 2020 USD ($) property	Mar. 31, 2021 USD ($) property	Mar. 31, 2020 USD ($) property	Dec. 31, 2021 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							$ (924,119,000)	$ 761,421,000
Gain on sales of real estate, net							0	$ 2,069,000
Number of properties disposed | property								18
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										$ 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										$ 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				92,000,000
Capital expenditure funding, amount funded							0
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings				230,000,000			5,000,000	$ 36,000,000		$ 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)
SHOP | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		$ 13,000,000
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
SHOP | Oakmont SHOP Portfolio | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		564,000,000
SHOP | Discovery SHOP Portfolio | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		334,000,000
Proceeds from sale of loans and preferred equity method investments		21,000,000
SHOP | Sonata SHOP Portfolio | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		64,000,000
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										21
Proceeds from sale of buildings								385,000,000		$ 428,000,000
Senior housing triple-net | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings		$ 7,000,000
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
Senior Housing Operating Portfolio and Senior Housing Triple-Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sales of real estate, net								$ 165,000,000
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			1	7		23
SHOP | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		2
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
Proceeds from sale of buildings					$ 94,000,000
Net cash provided by financing activities					$ 61,000,000
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				32
Proceeds from sale of buildings				$ 664,000,000
Net cash provided by financing activities				$ 410,000,000
SHOP | Sunrise Senior Housing Portfolio | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property									2
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
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						$ 115,000,000
SHOP | SLC SHOP Portfolio | Definitive Agreement Four | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from deposits on real estate sales									$ 3,000,000
SHOP | Oakmont SHOP Portfolio | Subsequent Event
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 | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		10
Number of preferred equity method investments sold | property		2
SHOP | Discovery SHOP Portfolio | Subsequent Event | Secured Loans
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of loan receivables | property		2
SHOP | Sonata SHOP Portfolio | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		5
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								18
Senior housing triple-net | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property		2
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
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property										11
Medical office | Subsequent Event
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		$ 10,000,000
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