Master Transactions and Cooperation Agreement with Brookdale (Details) $ in Millions	1 Months Ended				3 Months Ended							12 Months Ended
	Oct. 31, 2019 USD ($) property facility lease	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($) property	Sep. 30, 2019 property facility	Jun. 30, 2019 facility	Mar. 31, 2019 facility	Dec. 31, 2018 property facility	Sep. 30, 2018 facility	Jun. 30, 2018 facility	Mar. 31, 2018 facility	Dec. 31, 2018 property	Jan. 01, 2018 USD ($) property
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Payment to acquired noncontrolling interest | $		$ 63	$ 32
RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Ownership percentage (as a percent)				90.00%
Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold								19				19
Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets transitioned												37
Assets Leased to Others | RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count				58
Senior housing triple-net
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | facility							2			2
Senior housing triple-net | Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count				78
Disposition of properties, available for sale				32
Reduction in rent | $													$ 5
Number of properties with rent concessions													3
Total consideration for disposition of real estate | $				$ 35
Number of assets transitioned												17
Senior housing triple-net | Assets Leased to Others | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties acquired				2
SHOP
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | facility					1	1	9	2	11	8	2
SHOP | Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets transitioned												20
SHOP | Assets Leased to Others | RIDEA Facilities
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count				36
Total consideration for disposition of real estate | $				$ 240
SHOP | Assets Leased to Others | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of assets to be sold				4
CCRC JV [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Percentage of interest acquired				10.00%
CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investment ownership percentage					49.00%
Property count					15
Subsequent Event | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties acquired	1
Subsequent Event | Other Non-Reporting Segment [Member]
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed | facility	1
Subsequent Event | Other Non-Reporting Segment [Member] | Assets Leased to Others | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count	15
Subsequent Event | Senior housing triple-net | Assets Leased to Others
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count	43
Subsequent Event | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investment ownership percentage	49.00%
Subsequent Event | Brookedale MTCA
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties disposed	18
Cash proceeds | $	$ 385
Subsequent Event | Brookedale MTCA | 2019 Amended Master Lease
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Annual rent escalator	2.40%
Subsequent Event | Brookedale MTCA | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of properties acquired	13
Property count	15
Subsequent Event | Brookedale MTCA | Assets Leased to Others | 2019 Amended Master Lease
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Number of leases to be terminated | lease	1
Number of properties to be restructured	24
Percent of sales proceeds	6.50%
Number of properties to be reallocated	14
Future rent | $	$ 20
Capital investment | $	$ 35
Annual percent increase	7.00%
Capital investment term	5 years
Subsequent Event | Brookedale MTCA | Other Non-Reporting Segment [Member] | Assets Leased to Others | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Property count	13
Subsequent Event | Brookedale MTCA | CCRC JV
Collaborative Arrangement and Arrangement Other than Collaborative [Line Items]
Investment ownership percentage	51.00%
Interest acquired	51.00%
Purchase cost | $	$ 1,060
Management termination fee | $	$ 100
Number of assets to be sold	2