Earnings per share and shareholders' equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended					6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Dec. 19, 2013	Mar. 20, 2013	Mar. 19, 2013	Jun. 30, 2014 Stock appreciation rights (SARs) Common stock	Jun. 30, 2013 Stock appreciation rights (SARs) Common stock	Jul. 14, 2014 Subsequent event
Earnings per share, basic and diluted
Distributed earnings, Basic and diluted	$ 0.31	$ 0.31	$ 0.62	$ 0.62
Undistributed earnings, Basic and diluted	$ 0.10	$ 0.10	$ 0.24	$ 0.13
Earnings per share, Basic and diluted	$ 0.41	$ 0.41	$ 0.86	$ 0.75
Antidilutive effect of HEI common stock
Antidilutive effects of SARs shares that were not included in the computation of diluted EPS (in shares)								102,000	102,000
Equity forward transaction
Public offering related to equity forward transaction (in shares)							6,100,000
Sale of common stock related to equity forward transaction (in dollars per share)	$ 26.75		$ 26.75				$ 26.75
Underwriting discount (in dollars per share)	$ 1.00312		$ 1.00312
Closing price of common stock (in dollar per share)							$ 27.01
Offering related to underwriters exercising their over-allotment option under equity forward transaction (in shares)						900,000
Shares borrowed by forward counterparty from third party	7,000,000		7,000,000
Underwriting discount					$ 1.3
Capital shares reserved for future issuance, equity forward transaction	5,700,000		5,700,000
Forward sale price (in dollars per share)	$ 25.74688		$ 25.74688
Initial fair value (in dollars per share)	$ 0		$ 0
Cash in exchange of physical delivery of shares on settlement	136		136
Delivery of cash on settlement	5.0		5.0		32.1					23.9
Underwriting discount included in delivery of cash	$ 6		$ 6
Delivery of net shares on settlement	188,000		188,000		1,300,000					1,000,000