Dispositions of Real Estate and Discontinued Operations - 2021 Dispositions of Real Estate (Details)	1 Months Ended									3 Months Ended	12 Months Ended
	Jan. 31, 2022 USD ($) property	Sep. 30, 2021 loan	Jun. 30, 2021 USD ($) property	May 31, 2021 USD ($) property	Apr. 30, 2021 USD ($) property preferred_equity_investment	Mar. 31, 2021 USD ($) property	Feb. 28, 2021 USD ($) property	Jan. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Mar. 31, 2021 USD ($) property	Dec. 31, 2021 USD ($) property loan	Dec. 31, 2020 USD ($) property loan	Dec. 31, 2019 USD ($) property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain (loss) on sales of real estate, net											$ 190,590,000	$ 90,350,000	$ (40,000)
Number of assets classified as discontinued operations | property									1			1
Repayments of secured debt									$ 6,000,000
Carrying value of mortgages assumed by buyer in real estate dispositions											$ 143,676,000	$ 0	0
Number of loans sold | loan											6	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				2
Repayments of secured debt					$ 64,000,000	$ 39,000,000
Mezzanine
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of loans sold | loan		1
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													30,000,000
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													23,000,000
Sunrise Senior Housing Portfolio | Senior Housing Operating Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Capital expenditure funding, amount committed			$ 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 Investments | Mortgage Debt
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 Investments | 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	$ 283,000,000
Other Investments | 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	193,000,000
Senior Housing Operating Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings								230,000,000					181,000,000
Payments to acquire finance receivables								150,000,000
Gain (loss) on sales of real estate, net								59,000,000		$ 16,000,000
Senior Housing Operating Portfolio | 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
Senior Housing Operating Portfolio | 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
Senior Housing Operating Portfolio | 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
Senior Housing Operating Portfolio | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings											169,000,000	$ 190,000,000
Senior Housing Triple Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from sale of buildings													$ 26,000,000
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
Senior Housing Triple Net | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property												21
Proceeds from sale of buildings											24,000,000	$ 428,000,000
Senior Housing Operating Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property								16					18
Senior Housing Operating Portfolio | Sunrise Senior Housing Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property			2					32
Proceeds from sale of buildings								$ 664,000,000
Payments to acquire finance receivables								$ 410,000,000
Gain (loss) on sales of real estate, net											$ 7,000,000
Senior Housing Operating Portfolio | Oakmont SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					12
Senior Housing Operating Portfolio | Discovery SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					10
Gain (loss) on sales of real estate, net					$ 0
Number of preferred equity method investments sold | preferred_equity_investment					2
Senior Housing Operating Portfolio | Discovery SHOP Portfolio | Mezzanine
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of loans sold | property					2
Senior Housing Operating Portfolio | Sonata SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property					5
Senior Housing Operating Portfolio | SLC SHOP Portfolio
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property				7
Repayments of secured debt				$ 70,000,000
Senior Housing Operating Portfolio | 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 Operating Portfolio | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property											15	23
Senior Housing Operating Portfolio | Other Investments | Mortgage Debt
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property											1
Senior Housing Triple Net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property													2
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 sold | property			2
Proceeds from sale of buildings			$ 80,000,000
Gain (loss) 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 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 sold | property							8
Senior Housing Triple Net | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property											7
Medical Office, Hospital
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property				1
Proceeds from sale of buildings				$ 226,000,000
Gain (loss) 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 sold | property													11
Medical Office | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property											10	11
Proceeds from sale of buildings											$ 68,000,000
MOB Land Parcels | Other Investments
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property											1	2
Life science | Other Investments | Subsequent Event
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of assets sold | property	1
Proceeds from sale of buildings	$ 14,000,000