Acquisitions and Dispositions - Additional Information (Detail) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014
Business Acquisition [Line Items]
Proceeds from sale of business	$ 27	$ 38
Nonhospital Health Care [Member]
Business Acquisition [Line Items]
Cash paid for acquisition	169	83
Hospitals [Member]
Business Acquisition [Line Items]
Cash paid for acquisition	15	14
Real Estate and Other Investments [Member]
Business Acquisition [Line Items]
Pretax gain (loss) on sales of business	2	20
Proceeds from sale of business	$ 27	$ 38