Real Estate Transactions - Brookedale MTCA Transactions (Details) $ in Millions	1 Months Ended			12 Months Ended
	Mar. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Nov. 30, 2017 USD ($) property facility	Dec. 31, 2018 property	Jan. 01, 2018 USD ($) property
Real Estate [Line Items]
Percentage of interest acquired			10.00%
Consideration transferred | $			$ 95
Payment to acquired noncontrolling interest | $	$ 63	$ 32
Brookedale MTCA
Real Estate [Line Items]
Number of assets to be sold (in properties)				19
RIDEA Facilities
Real Estate [Line Items]
Ownership percentage (as a percent)			90.00%
Assets Leased to Others
Real Estate [Line Items]
Number of assets transitioned				37
Assets Leased to Others | RIDEA Facilities
Real Estate [Line Items]
Property count (in properties)			58
Senior housing triple-net | Assets Leased to Others
Real Estate [Line Items]
Property count (in properties)			78
Disposition of properties, available for sale (in properties)			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
Real Estate [Line Items]
Number of properties acquired (in properties) | facility			2
SHOP | Assets Leased to Others
Real Estate [Line Items]
Number of assets transitioned				20
SHOP | Assets Leased to Others | Brookedale MTCA
Real Estate [Line Items]
Number of assets to be sold (in properties)			4
SHOP | Assets Leased to Others | RIDEA Facilities
Real Estate [Line Items]
Property count (in properties)			36
Total consideration for disposition of real estate | $			$ 240