Supplemental Condensed Consolidating Financial Information and Other Collateral-Related Information - Schedule of Condensed Consolidating Statement of Cash Flows (Detail) - USD ($) $ 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
Cash flows from operating activities:
Net income (loss)	$ 641	$ 530	$ 795	$ 777	$ 1,085	$ 745	$ 791	$ 811	$ 2,743	$ 3,432	$ 2,696
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in operating assets and liabilities									(4,335)	(3,215)	(4,236)
Provision for doubtful accounts									4,039	3,257	3,913
Depreciation and amortization									2,131	1,966	1,904
Income taxes									433	123	(160)
Losses (gains) on sales of facilities	1	4	$ 1	1	15	2	$ 4	2	(8)	(23)	5
Losses on retirement of debt		$ 25				$ 2			39	4	135
Legal claim costs (benefits)										(246)	249
Legal claim costs											149
Amortization of debt issuance costs									31	34	35
Share-based compensation									270	251	239
Other									83	70	54
Net cash provided by (used in) operating activities									5,426	5,653	4,734
Cash flows from investing activities:
Purchase of property and equipment									(3,015)	(2,760)	(2,375)
Acquisition of hospitals and health care entities									(1,212)	(576)	(351)
Disposal of hospitals and health care entities									25	26	73
Change in investments									(73)	64	63
Other									(4)	6	7
Net cash used in investing activities									(4,279)	(3,240)	(2,583)
Cash flows from financing activities:
Issuance of long-term debt									1,502	5,400	5,548
Net change in revolving bank credit facilities									760	(110)	150
Repayment of long-term debt									(753)	(4,475)	(4,920)
Distributions to noncontrolling interests									(448)	(434)	(495)
Payment of debt issuance costs									(26)	(40)	(50)
Repurchases of common stock									(2,051)	(2,751)	(2,397)
Other									(45)	(98)	188
Net cash (used in) provided by financing activities									(1,061)	(2,508)	(1,976)
Change in cash and cash equivalents									86	(95)	175
Cash and cash equivalents at beginning of period				646				741	646	741	566
Cash and cash equivalents at end of period	732				646				732	646	741
Eliminations [Member]
Cash flows from operating activities:
Net income (loss)									(2,476)	(2,738)	(2,352)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Equity in earnings of affiliates									2,476	2,738	2,352
HCA Healthcare, Inc. Issuer [Member]
Cash flows from operating activities:
Net income (loss)									2,216	2,890	2,129
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in operating assets and liabilities										(25)	(12)
Income taxes									433	123	(160)
Losses on retirement of debt											122
Legal claim costs (benefits)											120
Legal claim costs											20
Amortization of debt issuance costs										1	3
Equity in earnings of affiliates									(2,476)	(2,738)	(2,352)
Other									78	71	66
Net cash provided by (used in) operating activities									251	322	(184)
Cash flows from financing activities:
Repayment of long-term debt											(1,632)
Repurchases of common stock									(2,051)	(2,751)	(2,397)
Changes in intercompany balances with affiliates, net									1,867	2,532	4,006
Other									(66)	(103)	207
Net cash (used in) provided by financing activities									(250)	(322)	184
Change in cash and cash equivalents									1
Cash and cash equivalents at end of period	1								1
HCA Inc. Issuer [Member]
Cash flows from operating activities:
Net income (loss)									(1,973)	(1,586)	(1,625)
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in operating assets and liabilities									(193)	39	44
Losses on retirement of debt									39	4	13
Legal claim costs (benefits)										(246)	129
Legal claim costs											129
Amortization of debt issuance costs									31	33	32
Other											3
Net cash provided by (used in) operating activities									(2,096)	(1,756)	(1,404)
Cash flows from financing activities:
Issuance of long-term debt									1,500	5,400	5,548
Net change in revolving bank credit facilities									760	(110)	150
Repayment of long-term debt									(628)	(4,358)	(3,189)
Payment of debt issuance costs									(26)	(40)	(50)
Changes in intercompany balances with affiliates, net									490	864	(1,055)
Net cash (used in) provided by financing activities									2,096	1,756	1,404
Subsidiary Guarantors [Member]
Cash flows from operating activities:
Net income (loss)									4,028	3,741	3,442
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in operating assets and liabilities									(2,437)	(2,180)	(2,786)
Provision for doubtful accounts									2,218	2,041	2,329
Depreciation and amortization									1,237	1,141	1,085
Losses (gains) on sales of facilities									(2)	4
Share-based compensation									270	251	239
Other											(5)
Net cash provided by (used in) operating activities									5,314	4,998	4,304
Cash flows from investing activities:
Purchase of property and equipment									(1,681)	(1,554)	(1,560)
Acquisition of hospitals and health care entities									(26)	(199)	(51)
Disposal of hospitals and health care entities									14	10	48
Change in investments									(1)	(15)	7
Other											(6)
Net cash used in investing activities									(1,694)	(1,758)	(1,562)
Cash flows from financing activities:
Repayment of long-term debt									(77)	(74)	(60)
Distributions to noncontrolling interests									(140)	(64)	(85)
Changes in intercompany balances with affiliates, net									(3,404)	(3,149)	(2,526)
Net cash (used in) provided by financing activities									(3,621)	(3,287)	(2,671)
Change in cash and cash equivalents									(1)	(47)	71
Cash and cash equivalents at beginning of period				113				160	113	160	89
Cash and cash equivalents at end of period	112				113				112	113	160
Subsidiary Non-Guarantors [Member]
Cash flows from operating activities:
Net income (loss)									948	1,125	1,102
Adjustments to reconcile net income (loss) to net cash provided by (used in) operating activities:
Change in operating assets and liabilities									(1,705)	(1,049)	(1,482)
Provision for doubtful accounts									1,821	1,216	1,584
Depreciation and amortization									894	825	819
Losses (gains) on sales of facilities									(6)	(27)	5
Other									5	(1)	(10)
Net cash provided by (used in) operating activities									1,957	2,089	2,018
Cash flows from investing activities:
Purchase of property and equipment									(1,334)	(1,206)	(815)
Acquisition of hospitals and health care entities									(1,186)	(377)	(300)
Disposal of hospitals and health care entities									11	16	25
Change in investments									(72)	79	56
Other									(4)	6	13
Net cash used in investing activities									(2,585)	(1,482)	(1,021)
Cash flows from financing activities:
Issuance of long-term debt									2
Repayment of long-term debt									(48)	(43)	(39)
Distributions to noncontrolling interests									(308)	(370)	(410)
Changes in intercompany balances with affiliates, net									1,047	(247)	(425)
Other									21	5	(19)
Net cash (used in) provided by financing activities									714	(655)	(893)
Change in cash and cash equivalents									86	(48)	104
Cash and cash equivalents at beginning of period				$ 533				$ 581	533	581	477
Cash and cash equivalents at end of period	$ 619				$ 533				$ 619	$ 533	$ 581