From where is the AP getting $1.5 trillion?

In an article that is burning up the tubes, the Associated Press' Erica Werner reported today that the House Democrats' tri-committee health-care reform proposal would cost "$1.5 trillion." Where does that figure come from? Werner doesn't break it down.

Yesterday, the Congressional Budget Office released a preliminary analysis scoring “specifications... reflected” in the bill released the same day. That analysis pegged those specs at a cost of a little over $1 trillion. The CBO went out of its way to point out that their estimates “are based on specifications provided by the tri-committee group rather than an analysis of the language released”; there are provisions included in the bill that the CBO did not include in their analysis.

So where did the AP's $1.5 trillion figure come from? Well, AP reports that “a House Democratic aide said the total bill would add up to about $1.5 trillion over 10 years.” So Werner got an anonymous source to give her a figure, and with no indication in her article that she consulted anyone inside or outside Congress to confirm that number, reported it as fact. Where is the extra $500 billion coming from on top of the CBO score? What provisions did the CBO not score? Why does this anonymous aide think those provisions cost half a trillion dollars? Does anyone else agree with him or her? Readers wouldn't know from the AP article.