Loans Receivable - Narrative (Details)			1 Months Ended											3 Months Ended				9 Months Ended	12 Months Ended
	Mar. 01, 2024 USD ($) loan	Dec. 31, 2023 USD ($)	Oct. 31, 2024 USD ($)	Jul. 31, 2024 USD ($) extension_option property	May 31, 2024 USD ($)	Feb. 29, 2024 USD ($)	Jan. 31, 2024 USD ($)	Oct. 31, 2023 USD ($)	Jun. 30, 2023	May 31, 2023 USD ($) loan	Apr. 30, 2023 USD ($) loan	Feb. 28, 2023 USD ($) loan	Jan. 31, 2021 USD ($) facility	Sep. 30, 2024 USD ($) property	Jun. 30, 2024 USD ($) property	Mar. 31, 2024 USD ($) property	Mar. 31, 2023 USD ($) property	Sep. 30, 2024 USD ($) loan	Dec. 31, 2022 USD ($)	Dec. 31, 2021 USD ($)
Loans Receivable:
Number of loans | loan																		6
Loans receivables, acquired	$ 124,000,000
Loans and leases receivable, remaining commitments														$ 56,000,000				$ 56,000,000
Financing receivable, after allowance for credit loss		$ 218,450,000												677,590,000				677,590,000
Credit loss reserve on unfunded loan commitments		700,000												4,900,000				4,900,000
Sunrise Senior Housing Portfolio
Loans Receivable:
Loans and leases receivable, remaining commitments		29,000,000				$ 0
Number of assets to be sold | facility													32
Proceeds from sale of property													$ 664,000,000
Investments in loans receivable													410,000,000
Capital expenditure funding, amount committed						1,000,000							$ 92,000,000						$ 40,000,000
Capital expenditure funding, cost of capital, percent committed													65.00%
Proceeds from the collection of loans receivable					$ 5,000,000	$ 69,000,000													$ 45,000,000	$ 246,000,000
Capital expenditure funding, amount funded		11,000,000
Financing receivable, after allowance for credit loss		131,000,000												58,000,000				$ 58,000,000
Sunrise Senior Housing Portfolio | Secured Overnight Financing Rate (SOFR)
Loans Receivable:
Loans receivable, conversion of basis spread on variable rate						0.10%			0.10%
Loans receivable, floor rate						9.00%
Sunrise Senior Housing Portfolio | Secured Overnight Financing Rate (SOFR), First Two Years
Loans Receivable:
Loans receivable, basis spread on variable rate						4.00%
Loan receivable, extended maturity term						2 years
Sunrise Senior Housing Portfolio | Secured Overnight Financing Rate (SOFR), Last Eighteen Months
Loans Receivable:
Loans receivable, basis spread on variable rate						5.00%
Loan receivable, extended maturity term						18 months
SHOP
Loans Receivable:
Number of assets to be sold | facility													16
Proceeds from sale of property													$ 230,000,000
Investments in loans receivable													$ 150,000,000
Loans receivable, extension fee												$ 1,000,000
Outpatient Medical Buildings
Loans Receivable:
Proceeds from sale of property				$ 674,000,000										674,000,000	$ 179,000,000	$ 29,000,000	$ 32,000,000
Investments in loans receivable				$ 405,000,000										$ 405,000,000
Number of properties sold | property				59										59	11	2	2
Loans receivable, number of extensions | extension_option				2
Loan receivable, period of extensions				12 months
Proceeds from loan originations				$ 1,000,000
Mark-to-market discount of real estate														$ (20,000,000)
Loans receivable, stated interest rate														6.25%				6.25%
Noncash or part noncash, interest income														$ 1,000,000				$ 1,000,000
Other non-reportable | Brookedale MTCA | Lessor Asset Under Operating Lease | CCRC JV
Loans Receivable:
Financing receivable, after allowance for credit loss		43,000,000												56,000,000				56,000,000
Minimum | Outpatient Medical Buildings
Loans Receivable:
Loans receivable, interest rate				0.060
Maximum | Outpatient Medical Buildings
Loans Receivable:
Loans receivable, interest rate				0.065
Secured Mortgage Loans
Loans Receivable:
Number of loans | loan	9
Loans receivable, outstanding balance	$ 89,000,000
Receivable with imputed interest														1,000,000				1,000,000
Secured Mortgage Loans | Other
Loans Receivable:
Proceeds from the collection of loans receivable								$ 21,000,000		$ 12,000,000	$ 14,000,000	$ 35,000,000
Number of secured loans | loan										2	1	1
Secured Mortgage Loans | Other | During June 2024 to December 2024
Loans Receivable:
Loans receivable, outstanding balance																		$ 12,000,000
Number of secured loans | loan																		1
Secured Mortgage Loans | Secured Overnight Financing Rate (SOFR) | Other
Loans Receivable:
Loans receivable, conversion of basis spread on variable rate										0.10%
Secured Mortgage Loans | LIBOR | Other
Loans Receivable:
Loans receivable, outstanding balance										$ 21,000,000
Number of secured loans | loan										1
Secured Mortgage Loans | SHOP
Loans Receivable:
Proceeds from the collection of loans receivable												$ 102,000,000
Loans receivable, floor rate							12.00%
Financing receivable, after allowance for credit loss		$ 48,000,000												48,000,000				$ 48,000,000
Loans receivable, extension fee							$ 1,000,000
Secured Mortgage Loans | SHOP | Secured Overnight Financing Rate (SOFR)
Loans Receivable:
Loans receivable, conversion of basis spread on variable rate							0.11%
Loans receivable, basis spread on variable rate												0.11%
Loans receivable, floor rate							7.00%
Secured Mortgage Loans | SHOP | Secured Overnight Financing Rate (SOFR), First Six Months
Loans Receivable:
Loans receivable, basis spread on variable rate												6.00%
Secured Mortgage Loans | SHOP | Secured Overnight Financing Rate (SOFR), Last Six Months
Loans Receivable:
Loans receivable, basis spread on variable rate												7.00%
Secured Mortgage Loans | Minimum
Loans Receivable:
Loans receivable, interest rate	0.0700
Secured Mortgage Loans | Maximum
Loans Receivable:
Loans receivable, interest rate	0.1000
Mezzanine loans
Loans Receivable:
Number of loans | loan	10
Loans receivable, outstanding balance	$ 36,000,000
Receivable with imputed interest														$ 3,000,000				$ 3,000,000
Mezzanine loans | Other | During May 2026 to May 2027
Loans Receivable:
Number of loans | loan																		1
Loans receivable, outstanding balance																		$ 2,000,000
Mezzanine loans | Other | During October 2024 to April 2026
Loans Receivable:
Number of loans | loan																		1
Loans receivable, outstanding balance																		$ 2,000,000
Mezzanine loans | Other | During June 2024 to June 2025
Loans Receivable:
Number of loans | loan																		1
Loans receivable, outstanding balance																		$ 1,000,000
Mezzanine loans | Other | Mezzanine Loan Maturity Due October 2025 | Subsequent Event
Loans Receivable:
Loans receivable, outstanding balance			$ 15,000,000
Loans receivable, stated interest rate			8.00%
Mezzanine loans | Minimum
Loans Receivable:
Loans receivable, interest rate	0.0800
Mezzanine loans | Maximum
Loans Receivable:
Loans receivable, interest rate	0.1000