ASSETS AND LIABILITIES HELD FOR SALE - Significant Disposals (Details) - USD ($) $ in Millions	3 Months Ended				6 Months Ended
	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Impairment charges						$ 2
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	$ (6)			$ 30	$ 86	34
Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	(2)			(3)	(15)	(9)
Houston | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	0			13	0	28
Philadelphia | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	(2)			2	(11)	(12)
MacNeal | Disposal Group, Disposed of by Sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	(4)			15	97	18
Gain on sale	95				95
Chicago-area | Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	1			1	(15)	(3)
Impairment charges	17	$ 17	$ 73
Aspen | Disposal Group, Held-for-sale, Not Discontinued Operations
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) from continuing operations, before income taxes	$ (3)			$ (4)	$ 0	$ (6)