Earnings per share and shareholders' equity (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013	Dec. 19, 2013	Mar. 20, 2013	Mar. 19, 2013
Earnings per share, basic and diluted
Distributed earnings, basic and diluted	$ 0.31	$ 0.31
Undistributed earnings, basic and diluted	$ 0.14	$ 0.03
Earnings per share, basic and diluted	$ 0.45	$ 0.34
Antidilutive effect of HEI common stock
Antidilutive effects of SARs shares that were not included in the computation of diluted EPS (in shares)		0
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
Underwriting discount (in dollars per share)	$ 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
Underwriting discount			$ 1.3
Common Stock, Capital Shares Reserved for Future Issuance, Equity Forward Transaction	5,700,000
Forward sale price (in dollars per share)	$ 25.74688
Initial fair value (in dollars per share)	$ 0
Cash in exchange of physical delivery of shares on settlement	139
Delivery of cash on settlement	6.0		32.1
Underwriting discount included in delivery of cash	$ 6
Delivery of net shares on settlement	220,000		1,300,000
Stock appreciation rights (SARs) | Common stock
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