I'd just like to point out it wouldn't be the first time something the US financed/created get out of their control.

For instance, it's a well known & proven fact that Al Qaeda was originally financed by the US as a rebel group used to overthrow the last remains of soviet-like communism in Afghanistan, and then shit went down. So, considering our rulers do not seem to learn from previous mistakes or generally show great interest in the lives of their fellow human beings, I don't think it's unconceivable that they did finance ISIS for some geopolitical purpose in the early beginning of that group.

Edit : nvm, it's actually written in those articles.