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								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Earnings Per Share [Abstract]
Net income attributable to HCA Healthcare, Inc.	$ 474	$ 426	$ 657	$ 659	$ 920	$ 618	$ 658	$ 694	$ 2,216	$ 2,890	$ 2,129
Weighted average common shares outstanding									362,305	383,591	414,193
Effect of dilutive incremental shares									9,916	12,260	12,528
Shares used for diluted earnings per share									372,221	395,851	426,721
Basic earnings per share	$ 1.34	$ 1.18	$ 1.79	$ 1.78	$ 2.46	$ 1.63	$ 1.70	$ 1.75	$ 6.12	$ 7.53	$ 5.14
Diluted earnings per share	$ 1.30	$ 1.15	$ 1.75	$ 1.74	$ 2.39	$ 1.59	$ 1.65	$ 1.69	$ 5.95	$ 7.30	$ 4.99