Income Taxes - Schedule of Reconciliation of Federal Statutory Rate to Effective Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Federal statutory rate	35.00%	35.00%	35.00%
State income taxes, net of federal tax benefit	2.20%	2.10%	1.60%
Change in liability for uncertain tax positions		(1.00%)	0.20%
Tax benefit from settlements of employee equity awards	(2.00%)	(3.60%)
Impact of rate change on deferred tax balances	7.80%
Other items, net	(0.50%)	(0.20%)	0.40%
Effective income tax rate on income applicable to HCA Healthcare, Inc.	42.50%	32.30%	37.20%
Income attributable to noncontrolling interests from consolidated partnerships	(5.10%)	(3.60%)	(5.30%)
Effective income tax rate on income before income taxes	37.40%	28.70%	31.90%