Other related-party transactions (Details) - Affiliated Entity - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Hawaii Medical Service Association (HMSA) | Gross costs
Related Party Transaction [Line Items]
Expenses from related party transactions	$ 30	$ 25	$ 23
Hawaii Medical Service Association (HMSA) | Gross costs | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	23	20	18
Hawaii Medical Service Association (HMSA) | Net expense
Related Party Transaction [Line Items]
Expenses from related party transactions	21	18	17
Hawaii Medical Service Association (HMSA) | Net expense | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	14	13	12
Hawaii Dental Service (HDS) | Gross costs
Related Party Transaction [Line Items]
Expenses from related party transactions	3	3	3
Hawaii Dental Service (HDS) | Gross costs | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	2	2	2
Hawaii Dental Service (HDS) | Net expense
Related Party Transaction [Line Items]
Expenses from related party transactions	2	2	2
Hawaii Dental Service (HDS) | Net expense | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from related party transactions	$ 1	$ 1	$ 1