Impairments of Real Estate (Details)	3 Months Ended			12 Months Ended
	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Dec. 31, 2019 USD ($) property	Jan. 31, 2020 property	Oct. 31, 2019 property
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property						3
Property count | property							15
Net real estate				$ 12,667,429,000	$ 11,119,758,000
Impairments and loan loss reserves (recoveries), net				23,160,000	42,909,000	$ 17,708,000
Asset impairment charge						18,000,000
Goodwill, impairment loss				0	0	0
Goodwill				18,000,000	18,000,000
Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Goodwill, impairment loss	$ 22,000,000	$ 7,000,000		29,000,000
Goodwill				0	29,000,000
Discontinued Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net					$ 201,000,000
Asset impairment charge						$ 9,000,000
Medical Office
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of real estate				$ 22,000,000
Number of real estate properties impaired | property				3	5	3
Property count | property				4
Impairments and loan loss reserves (recoveries), net						$ 4,000,000
Number of properties intended to be demolished | property						1
Number of real estate properties impaired, candidates for potential sale | property						2
Medical Office | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property				3
Medical Office | Held-for-use
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property				1
Senior Housing Operating Portfolio
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of real estate				$ 4,000,000
Number of real estate properties impaired | property				1	42	27
Impairments and loan loss reserves (recoveries), net			$ 10,000,000
Number of real estate properties impaired, candidates for potential sale | property						1
Life Science
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net					$ 15,000,000
Number of properties intended to be demolished | property					1
Senior Housing Triple Net, SHOP, and MOB
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net					$ 210,000,000
Senior Housing Triple Net
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property					5	8
Property count | property								43
MOB Land Parcels
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property					1
Senior Housing Triple Net, SHOP, MOB, and Other Non-Reportable
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net						$ 194,000,000
Senior Housing Triple Net, SHOP, MOB, and Other Non-Reportable | Discontinued Operations
Impaired Long-Lived Assets Held and Used [Line Items]
Impairments and loan loss reserves (recoveries), net						$ 189,000,000
Other Non-Reporting Segment
Impaired Long-Lived Assets Held and Used [Line Items]
Number of real estate properties impaired | property						1
Impairments 2021 | Medical Office | Held-for-sale
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of real estate				$ 5,000,000
Net real estate				14,000,000
Impairments 2021 | Medical Office | Held-for-use
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment of real estate				17,000,000
Impairments 2021 | Senior Housing Operating Portfolio
Impaired Long-Lived Assets Held and Used [Line Items]
Real estate held-for-sale				16,000,000
Aggregate carrying value before impairment				$ 20,000,000
Shop Assets, Senior Housing Triple-net Assets, MOBs, and Other Non-Reportable Asset
Impaired Long-Lived Assets Held and Used [Line Items]
Real estate held-for-sale					$ 750,000,000	$ 223,000,000
Aggregate carrying value before impairment					960,000,000	416,000,000
Minimum
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range					$ 13,000	$ 24,000
Terminal capitalization rate					5.50%
Discount rates					8.00%
Market capitalization rate						4.97%
Maximum
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range					$ 300,000	$ 125,000
Terminal capitalization rate					7.50%
Discount rates					9.50%
Market capitalization rate						8.27%
Weighted Average
Impaired Long-Lived Assets Held and Used [Line Items]
Impairment calculation price range					$ 164,000	$ 73,000
Market capitalization rate						6.22%