Earnings Per Share - Schedule of Computations of Basic and Diluted Earnings Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Earnings Per Share [Abstract]
Net income attributable to HCA Holdings, Inc.	$ 618	$ 449	$ 1,970	$ 1,547
Weighted average common shares outstanding	378,199	414,939	386,968	417,146
Effect of dilutive incremental shares	11,393	11,502	12,609	13,208
Shares used for diluted earnings per share	389,592	426,441	399,577	430,354
Basic earnings per share	$ 1.63	$ 1.08	$ 5.09	$ 3.71
Diluted earnings per share	$ 1.59	$ 1.05	$ 4.93	$ 3.60