Dispositions of Real Estate and Discontinued Operations - Narrative (Details)	1 Months Ended									3 Months Ended		12 Months Ended	15 Months Ended
	Apr. 30, 2022 USD ($) property	Feb. 28, 2022 USD ($)	Jan. 31, 2022 USD ($) property	Jun. 30, 2021 USD ($) 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 ($) property	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($) property	Dec. 31, 2021 USD ($) property	Mar. 31, 2022 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net										$ 3,856,000	$ 0
Impairment of real estate										0	$ 0
Planned MOB Demolition, Tenant Relocation and Other Costs
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expense on other										$ 14,000,000
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				2
Repayments of secured debt						$ 64,000,000	$ 39,000,000
Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net												$ 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 (loss) on sales of real estate, net												58,000,000
Sunrise Senior Housing Portfolio | SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital expenditure funding, amount committed		$ 47,000,000		$ 56,000,000					$ 92,000,000
Capital expenditure funding, amount funded													$ 400,000
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
Other Dispositions
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												$ 36,000,000
Other Dispositions | Mortgage Debt
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed | property												1
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings									230,000,000
Gain (loss) on sales of real estate, net									59,000,000		$ 16,000,000
Payments to acquire finance receivables									150,000,000
SHOP | Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings											$ 5,000,000
Number of assets to be sold | property											1
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 (loss) 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 (loss) 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 (loss) on sales of real estate, net						$ 3,000,000
SHOP | Other Dispositions
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings												$ 169,000,000
Senior Housing Triple Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings												24,000,000
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 (loss) 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 (loss) on sales of real estate, net								$ 33,000,000
Life Science
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property			1
Proceeds from sale of buildings			$ 14,000,000
Gain (loss) on sales of real estate, net			$ 4,000,000
Medical Office Buildings
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings												$ 68,000,000
Number of assets to be sold | property												10
Medical Office Buildings | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties sold | property	1
Proceeds from sale of buildings	$ 13,000,000
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets to be sold | property									16			15
SHOP | Sunrise Senior Housing Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings									$ 664,000,000
Number of assets to be sold | property									32
Payments to acquire finance receivables									$ 410,000,000
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]
Gain (loss) on sales of real estate, net						$ 0
Number of assets to be sold | property						10
Number of preferred equity method investments 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 (loss) on sales of real estate, net					1,000,000
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												7
Senior Housing Triple Net | Sunrise Senior Housing Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings				80,000,000
Gain (loss) on sales of real estate, net				$ 22,000,000
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
Medical Office, Hospital
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings					226,000,000
Gain (loss) on sales of real estate, net					$ 172,000,000
Number of assets to be sold | property					1