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		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Earnings Per Share [Abstract]
Net income attributable to HCA Holdings, Inc.	$ 507	$ 483	$ 1,098	$ 830
Weighted average common shares outstanding	416,407	438,833	418,267	440,482
Effect of dilutive incremental shares	12,962	14,176	14,062	14,738
Shares used for diluted earnings per share	429,369	453,009	432,329	455,220
Basic earnings per share	$ 1.22	$ 1.10	$ 2.63	$ 1.88
Diluted earnings per share	$ 1.18	$ 1.07	$ 2.54	$ 1.82