Variable Interest Entities - Narrative (Details) $ in Millions			1 Months Ended						3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2020 USD ($) loan property joint_venture tenant investment	Jan. 31, 2020 property	Oct. 31, 2021 property	Sep. 30, 2021 joint_venture loan	Jun. 30, 2021 property	May 31, 2021 property	Apr. 30, 2021 property	Jan. 31, 2021 property	Sep. 30, 2021 property joint_venture	Sep. 30, 2020 property	Sep. 30, 2021 property joint_venture facility	Sep. 30, 2020 property	Dec. 31, 2020 USD ($) loan property joint_venture tenant
Variable Interest Entity [Line Items]
Number of investments in senior housing development joint ventures | investment	2
Number of loans sold				1							5		3
Number of properties disposed												18
Term of facility (in years)											1 month		1 month
Number of properties acquired											0
Exchange accommodation titleholder, real estate, carrying value | $	$ 813												$ 813
Brookedale MTCA
Variable Interest Entity [Line Items]
Number of properties disposed		18											18
CCRC JV
Variable Interest Entity [Line Items]
Investment ownership percentage	49.00%	49.00%				49.00%							49.00%
CCRC JV | Brookedale MTCA
Variable Interest Entity [Line Items]
Number of assets to be sold						2
VIE tenant - operating leases
Variable Interest Entity [Line Items]
Number of properties leased (in properties)	2												2
Number of VIE tenants (in tenants) | tenant	1												1
Unconsolidated Variable Interest Entities
Variable Interest Entity [Line Items]
Number of unconsolidated joint ventures (in joint ventures) | joint_venture	4			1					1		1		4
Number of VIE borrowers with marketable debt securities (in joint ventures) | joint_venture	1			1					1		1		1
Number of properties leased (in properties)	2												2
Number of loans to VIE borrowers (in loans) | loan	1												1
Hcp Ventures V
Variable Interest Entity [Line Items]
VIE ownership percentage											51.00%
Life science joint ventures
Variable Interest Entity [Line Items]
VIE ownership percentage											99.00%
MSREI JV
Variable Interest Entity [Line Items]
VIE ownership percentage											51.00%
Consolidated Lessees VIE
Variable Interest Entity [Line Items]
Number of properties leased (in properties)	7												7
Number of assets to be sold											7
DownREIT Partnerships
Variable Interest Entity [Line Items]
Number of controlling ownership interest entities as a managing member | joint_venture											7
SHOP
Variable Interest Entity [Line Items]
Number of assets to be sold								16	8	4	15	13	23
SHOP | Sunrise Senior Housing Portfolio
Variable Interest Entity [Line Items]
Number of assets to be sold					2			32
SHOP | Discovery SHOP Portfolio
Variable Interest Entity [Line Items]
Number of assets to be sold							10
Number of preferred equity method investments sold							2
SHOP | Discovery SHOP Portfolio | Secured Loans
Variable Interest Entity [Line Items]
Number of loans sold							2
Senior Housing Triple-Net
Variable Interest Entity [Line Items]
Number of assets to be sold									4		7	18
Senior Housing Triple-Net | Sunrise Senior Housing Portfolio
Variable Interest Entity [Line Items]
Number of assets to be sold					2
Senior Housing Triple-Net | Loans receivable
Variable Interest Entity [Line Items]
Number of properties disposed | facility											7
Term of facility (in years)											5 years
Medical office
Variable Interest Entity [Line Items]
Number of assets to be sold									3	4	7	7	11
Number of properties acquired													7
Medical office | Subsequent Event
Variable Interest Entity [Line Items]
Number of properties acquired			2
Medical Office, Hospital
Variable Interest Entity [Line Items]
Number of assets to be sold						1
Number of properties acquired													1
Life science
Variable Interest Entity [Line Items]
Number of properties acquired													3