Variable Interest Entities and Investment in Unconsolidated Ventures - Equity Method Investments (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Statement of Operations Information
Resident fee revenue	$ 1,354	$ 1,133	$ 964
Facility operating expenses	(946)	(779)	(679)
Net income (loss)	(81)	(4)	$ (18)
Balance Sheet Information
Current assets	164	128
Noncurrent assets	4,050	3,932
Current liabilities	672	1,153
Noncurrent liabilities	$ 2,813	$ 2,215