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, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to HCA Healthcare, Inc.	$ 759	$ 426	$ 2,723	$ 1,742
Weighted average common shares outstanding	345,823	360,170	348,411	365,398
Effect of dilutive incremental shares	7,816	9,664	7,713	9,615
Shares used for diluted earnings per share	353,639	369,834	356,124	375,013
Basic earnings	$ 2.20	$ 1.18	$ 7.82	$ 4.77
Diluted earnings	$ 2.15	$ 1.15	$ 7.65	$ 4.64