Real Estate Transactions - 2021 Real Estate Investment Acquisitions (Details) $ in Millions	1 Months Ended										12 Months Ended
	Jan. 31, 2022 USD ($)	Dec. 31, 2021 USD ($) a property	Oct. 31, 2021 USD ($) property	Sep. 30, 2021 USD ($) property	Jul. 31, 2021 USD ($) property	Jun. 30, 2021 USD ($) property	Apr. 30, 2021 USD ($) property	Feb. 28, 2021 USD ($) property	Dec. 31, 2020 USD ($) property	Apr. 30, 2020 USD ($)	Dec. 31, 2021 USD ($) a property	Dec. 31, 2020 property
MASSACHUSETTS
Real Estate [Line Items]
Payments to acquire real estate									$ 54
CALIFORNIA
Real Estate [Line Items]
Area of land | a		12									12
Payments to acquire land											$ 128
Number of adjacent sites currently held | property											2
Medical Office
Real Estate [Line Items]
Number of properties acquired | property											2	7
Medical Office | Mortgage Debt
Real Estate [Line Items]
Face amount							$ 142
Medical Office | TENNESSEE
Real Estate [Line Items]
Number of properties acquired | property								1
Payments to acquire real estate								$ 13
Medical Office | COLORADO
Real Estate [Line Items]
Number of properties acquired | property							1
Payments to acquire real estate							$ 38
Medical Office | UNITED STATES
Real Estate [Line Items]
Number of properties acquired | property							14
Payments to acquire real estate							$ 371
Medical Office | FLORIDA
Real Estate [Line Items]
Number of properties acquired | property						1
Payments to acquire real estate						$ 16
Medical Office | KANSAS
Real Estate [Line Items]
Number of properties acquired | property					1
Payments to acquire real estate					$ 50
Medical Office | NEW JERSEY
Real Estate [Line Items]
Number of properties acquired | property					3
Payments to acquire real estate					$ 155
Medical Office | TEXAS
Real Estate [Line Items]
Number of properties acquired | property				2					1
Payments to acquire real estate				$ 60					$ 34
Medical Office | MASSACHUSETTS
Real Estate [Line Items]
Number of properties acquired | property			1
Payments to acquire real estate			$ 80
Medical Office | WASHINGTON
Real Estate [Line Items]
Number of properties acquired | property			1
Payments to acquire real estate			$ 43
Medical Office | LOUISIANA
Real Estate [Line Items]
Number of properties acquired | property			1
Payments to acquire real estate			$ 34
Life science
Real Estate [Line Items]
Number of properties acquired | property												3
Life science | MASSACHUSETTS
Real Estate [Line Items]
Number of properties acquired | property		2		3					3
Payments to acquire real estate		$ 45	73	$ 180					$ 610	$ 320
Life science | MASSACHUSETTS | Subsequent Event
Real Estate [Line Items]
Payments to acquire real estate	$ 72
Life science | MASSACHUSETTS | Mooney Street Parcels
Real Estate [Line Items]
Payments to acquire real estate			123
Life science | MASSACHUSETTS | 25 Spinelli
Real Estate [Line Items]
Payments to acquire real estate			34
Life science | MASSACHUSETTS | 68 Moulton
Real Estate [Line Items]
Payments to acquire real estate			18
Life science | CALIFORNIA
Real Estate [Line Items]
Payments to acquire real estate			$ 20
Life science | CALIFORNIA | Subsequent Event
Real Estate [Line Items]
Payments to acquire real estate	$ 24