Bank segment - Income statement data (Details) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Noninterest income
Noninterest income	$ 550,412			$ 725,111			$ 1,701,967	$ 1,962,922
Noninterest expense
Income before income taxes	79,521			78,693			179,447	189,426
Income taxes	14,018			14,803			30,691	36,390
Net income	65,503			63,890			148,756	153,036
Other comprehensive income (loss), net of tax (benefits)	1,440	$ (332)	$ 18,212	3,297	$ 13,699	$ 9,241	19,320	26,237
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	66,472			66,716			166,659	177,856
COVID-19 related costs	700						4,500
Incremental compensation expense							2,400
Enhanced cleaning and sanitation costs							1,700
American Savings Bank (ASB)
Interest and dividend income
Interest and fees on loans	52,419			59,260			161,505	175,740
Interest and dividends on investment securities	7,221			7,599			22,939	25,762
Total interest and dividend income	59,640			66,859			184,444	201,502
Interest expense
Interest on deposit liabilities	2,287			4,384			8,945	12,923
Interest on other borrowings	61			422			449	1,361
Total interest expense	2,348			4,806			9,394	14,284
Net interest income	57,292			62,053			175,050	187,218
Provision for credit losses	13,970			3,315			39,504	17,873
Net interest income after provision for credit losses	43,322			58,738			135,546	169,345
Noninterest income
Total noninterest income	19,004			16,342			57,927	46,438
Noninterest expense
Compensation and employee benefits	26,431			25,364			77,287	76,626
Occupancy	5,693			5,694			16,402	15,843
Data processing	3,366			3,763			11,052	11,353
Services	2,624			2,829			7,907	7,861
Equipment	2,001			2,163			6,630	6,416
Office supplies, printing and postage	1,187			1,297			3,577	4,320
Marketing	727			1,142			1,908	3,455
FDIC insurance	714			(5)			1,567	1,249
Other expense1	4,556			3,676			15,813	12,049
Total noninterest expense	47,299			45,923			142,143	139,172
Income before income taxes	15,027			29,157			51,330	76,611
Income taxes	2,877			6,269			9,405	15,868
Net income	12,150			22,888			41,925	60,743
Other comprehensive income (loss), net of tax (benefits)	1,393			3,809			20,960	24,336
Comprehensive income attributable to Hawaiian Electric Industries, Inc.	13,543			26,697			62,885	85,079
American Savings Bank (ASB) | Fees from other financial services
Noninterest income
Noninterest income	4,233			5,085			11,906	14,445
American Savings Bank (ASB) | Fee income on deposit liabilities
Noninterest income
Noninterest income	3,832			5,320			11,842	15,402
American Savings Bank (ASB) | Fee income on other financial products
Noninterest income
Noninterest income	1,524			1,706			4,608	5,129
American Savings Bank (ASB) | Bank-owned life insurance
Noninterest income
Noninterest income	1,965			1,660			4,432	6,309
American Savings Bank (ASB) | Mortgage banking income
Noninterest income
Noninterest income	7,681			1,490			15,933	3,080
American Savings Bank (ASB) | Gain on sale of investment securities, net
Noninterest income
Noninterest income	0			653			9,275	653
American Savings Bank (ASB) | Other income, net
Noninterest income
Noninterest income	$ (231)			$ 428			$ (69)	$ 1,420