Acquisitions and Dispositions - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) Hospital	Dec. 31, 2016 USD ($) Hospital	Dec. 31, 2015 USD ($) Hospital
Business Acquisition [Line Items]
Number of hospitals purchased | Hospital	8	3	1
Proceeds from sale of business	$ 25	$ 26	$ 73
Real Estate and Other Investments [Member]
Business Acquisition [Line Items]
Pretax gain (loss) on sales of business	8	23	(5)
Pretax gain (loss) after tax	5	19	3
Proceeds from sale of business	25	26	73
Hospitals [Member]
Business Acquisition [Line Items]
Aggregate purchase price	1,000	343	15
Nonhospital Health Care [Member]
Business Acquisition [Line Items]
Aggregate purchase price	212	233	336
Other [Member]
Business Acquisition [Line Items]
Fair value of identifiable net assets of acquired entities	$ 693	$ 41	$ 323