Document and Entity Information - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2019	Feb. 20, 2020	Jun. 28, 2019
Document and Entity Information
Entity Registrant Name	FIRST HAWAIIAN, INC.
Entity Central Index Key	0000036377
Document Type	10-K
Document Annual Report	true
Document Transition Report	false
Document Period End Date	Dec. 31, 2019
Entity File Number	001-14585
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	99-0156159
Entity Address, Address Line One	999 Bishop Street, 29th Floor
Entity Address, City or Town	Honolulu
Entity Address, State or Province	HI
Entity Address, Postal Zip Code	96813
City Area Code	808
Local Phone Number	525-7000
Title of 12(b) Security	Common Stock, par value $0.01 per share
Trading Symbol	FHB
Security Exchange Name	NASDAQ
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 3.5
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		130,350,725
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	FY