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Summary of Significant Accounting Policies (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Jan. 31, 2017
Accounting Policies [Abstract]    
Residency agreement term, minimum 30 days  
Residency agreement term, maximum 1 year  
Maximum period available for occupancy from cessation of significant construction activity 1 year  
Maximum useful life of building and improvements 60 years  
RIDEA II    
Schedule of Equity Method Investments    
Investment ownership percentage 40.00% 40.00%
Fair value of equity investment   $ 107
Equity method investments   $ 121
Pro Forma | Difference between Revenue Guidance in Effect before and after Topic 606 | ASU 2014-09    
Schedule of Equity Method Investments    
Cumulative effect of change on beginning retained earnings $ 30  
Pro Forma | Difference between Revenue Guidance in Effect before and after Topic 606 | ASU 2014-09 | RIDEA II    
Schedule of Equity Method Investments    
Equity method investments $ 91