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, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Net income attributable to HCA Holdings, Inc.	$ 449	$ 518	$ 1,547	$ 1,348
Weighted average common shares outstanding	414,939	432,617	417,146	437,832
Effect of dilutive incremental shares	11,502	14,643	13,208	14,706
Shares used for diluted earnings per share	426,441	447,260	430,354	452,538
Basic earnings per share	$ 1.08	$ 1.20	$ 3.71	$ 3.08
Diluted earnings per share	$ 1.05	$ 1.16	$ 3.60	$ 2.98