Enough to pay them more than £30m extra in interest a year. Now they've been ordered to repay you, with interest.
Hoarding your moneyQuoted in the Mail, a Government source says the Big Six will be ordered to pay interest to those with a credit surplus. If they don't, then they could be fined. As energy bills and monthly direct debits have grown - the average duel fuel bill now tips £1,500 - so have energy industry cashpiles.
"The minister will urge energy companies to agree to new industry wide best practice for this winter and will push them to pay interest to customers who are in surplus," a Government source told the paper.
A meeting between energy minister Greg Barker and energy companies is thought to happen soon. The Government remains under pressure to show it is sensitive to consumer worry about the rising cost of energy, as well as responding to Labour's promise to freeze energy prices.
20m cash injectionsNpower told AOL Money it automatically refunds customers who have built a credit of more than £60 - though this is only done once a year, on the anniversary of when each account was opened - while the threshold is £100 for SSE.
20m UK consumers pay their energy bills via direct debit, with an average credit of around £100 on each account, it's estimated. Very few consumers request a cash rebate once credit is built up.
On the other hand, there's something to be said to building up a credit, especially after the hard winter of 2012/13 - as long as interest is paid. What would you prefer? Some cash saved up in advance - or in your pocket?
Meanwhile prices continue to climb. Scottish Power joined other energy suppliers recently by announcing an 8.6% hike in prices. From 6 December, 2.2 million customers will see a £118 hike in their bills, a total rise of £137 over the last year alone, according to Moneysupermarket.com.