Basis of presentation (Details) - HECO (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Dec. 31, 2010
Consolidated Balance Sheet
Total assets	$ 9,904,827	$ 9,594,477
Retained earnings	233,218	198,397	178,667
Total capitalization and liabilities	9,904,827	9,594,477
Consolidated Statement of Changes in Common Stock Equity
Retained earnings	233,218	198,397	178,667
Hawaiian Electric Company, Inc. and Subsidiaries
Consolidated Balance Sheet
Prepayments and other	64,006	36,667
Total current assets	719,192	650,269
Total assets	4,961,715	4,674,007
Retained earnings	921,309	881,041	851,613
Common stock equity	1,443,338	1,402,841	1,334,155
Total capitalization	2,625,500	2,437,704
Taxes accrued	235,302	230,076
Total current liabilities	577,062	564,992
Total capitalization and liabilities	4,961,715	4,674,007
Consolidated Statement of Changes in Common Stock Equity
Retained earnings	921,309	881,041	851,613
Common stock equity	1,443,338	1,402,841	1,334,155
As previously filed
Consolidated Balance Sheet
Total assets		9,592,731
Retained earnings		201,640	181,910
Total capitalization and liabilities		9,592,731
Consolidated Statement of Changes in Common Stock Equity
Retained earnings		201,640	181,910
As previously filed | Hawaiian Electric Company, Inc. and Subsidiaries
Consolidated Balance Sheet
Prepayments and other		34,602
Total current assets		648,204
Total assets		4,671,942
Retained earnings		884,284	854,856
Common stock equity		1,406,084	1,337,398
Total capitalization		2,440,947
Taxes accrued		224,768
Total current liabilities		559,684
Total capitalization and liabilities		4,671,942
Consolidated Statement of Changes in Common Stock Equity
Retained earnings		884,284	854,856
Common stock equity		1,406,084	1,337,398
Difference
Consolidated Balance Sheet
Total assets		1,746
Retained earnings		(3,243)	(3,243)
Total capitalization and liabilities		1,746
Consolidated Statement of Changes in Common Stock Equity
Retained earnings		(3,243)	(3,243)
Difference | Hawaiian Electric Company, Inc. and Subsidiaries
Consolidated Balance Sheet
Prepayments and other		2,065
Total current assets		2,065
Total assets		2,065
Retained earnings		(3,243)	(3,243)
Common stock equity		(3,243)	(3,243)
Total capitalization		(3,243)
Taxes accrued		5,308
Total current liabilities		5,308
Total capitalization and liabilities		2,065
Consolidated Statement of Changes in Common Stock Equity
Retained earnings		(3,243)	(3,243)
Common stock equity		$ (3,243)	$ (3,243)