Dispositions of Real Estate and Discontinued Operations - 2016 Dispositions (Details) $ in Millions	1 Months Ended		3 Months Ended				12 Months Ended
	Mar. 31, 2017 USD ($) facility	Jan. 31, 2017 USD ($) facility	Dec. 31, 2018 facility	Sep. 30, 2018 facility	Jun. 30, 2018 facility	Mar. 31, 2018 facility	Dec. 31, 2017 facility	Dec. 31, 2016 USD ($) facility
Post-acute/skilled | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)								5
Senior housing triple-net
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)	64				2		4	7
Total consideration for disposition of real estate | $	$ 1,125							$ 88
Senior housing triple-net | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)								2
Post-acute/skilled and SH NNN | Building
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration for disposition of real estate | $								$ 130
Life science
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)		4		4				5
Total consideration for disposition of real estate | $		$ 76						$ 386
Medical office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)			2	2			4	3
Total consideration for disposition of real estate | $								$ 20
SHOP
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of properties disposed (in facilities)			2	11	8	2	5	3
Total consideration for disposition of real estate | $								$ 41