Termination of proposed merger and other matters (Details)		1 Months Ended	3 Months Ended							12 Months Ended			25 Months Ended
	Jul. 21, 2016 application	May 31, 2016 application	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2016 lawsuit	Jul. 19, 2016 USD ($)
Business Acquisition [Line Items]
Number of additional public utility applications submitted | application		2
Number of public utility applications withdrawn | application	3
Number of lawsuits dismissed | lawsuit													7
Hawaiian Electric Company, Inc. and Subsidiaries
Business Acquisition [Line Items]
Merger termination, expenses recognized				$ 1,000,000	$ 1,000,000
NextEra Energy, Inc Merger
Business Acquisition [Line Items]
Merger contract termination fee			$ 90,000,000											$ 90,000,000
Maximum expenses paid to party for cancellation of merger														$ 5,000,000
Gain (loss) recognized, merger termination										$ 60,000,000
Merger termination, merger-and-spin-off related expenses, net of taxes			(64,000,000)	$ 2,000,000	$ 2,000,000	$ 2,000,000	$ 2,000,000	$ 7,000,000	$ 5,000,000	$ 6,000,000	$ 16,000,000	$ 5,000,000
Merger termination, termination fee			55,000,000
Merger termination, insurance reimbursements			3,000,000
Recognition of previously disallowed merger and acquisition expenses			$ 8,000,000