Related party transactions (Details) - Affiliated Entity - Hawaii Medical Service Association (HMSA) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
HMSA costs
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 8	$ 6	$ 22	$ 18
HMSA costs | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from transactions with related party	6	5	17	15
HMSA expense
Related Party Transaction [Line Items]
Expenses from transactions with related party	6	4	16	13
HMSA expense | Hawaiian Electric Company, Inc. and Subsidiaries
Related Party Transaction [Line Items]
Expenses from transactions with related party	$ 4	$ 3	$ 11	$ 9