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, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Earnings Per Share [Abstract]
Net income attributable to HCA Healthcare, Inc.	$ 820	$ 657	$ 1,964	$ 1,316
Weighted average common shares outstanding	348,615	365,847	349,726	368,056
Effect of dilutive incremental shares	6,424	9,491	7,662	9,591
Shares used for diluted earnings per share	355,039	375,338	357,388	377,647
Basic earnings	$ 2.35	$ 1.79	$ 5.62	$ 3.58
Diluted earnings	$ 2.31	$ 1.75	$ 5.50	$ 3.48