The ACA it is hoped will cut expenditures by the Federal government by several of its features. You are correct in mentioning some savings are to come by better fraud detection. The estimate is that this is only about 1% of the savings to be generated, at 4.9 billion of the 424 billion savings. This ability to detect fraud is one reason electronic records are being required. However, the data which the government is able to collect is not adequate to find fraud at this time.
The majority of the savings is anticipated to come from elimination of the overpayment to the Medicare advantage programs and adjustments in the payment schedules to providers other than physicians which together account for 350 billion in savings. The medicare advantage programs are paid an extra premium by the government with the expectation that their tighter controls would reduce costs. In fact these advantage programs are costing more per insured than traditional medicare and provide less choice of doctors and hospitals (it pays the providers less than traditional medicare) Guess who is pocketing that extra money and not saving the government anything? So the ACA levels the payment to the insurance company that offers the advantage program to that of basic medicare cost. If the carrier can be more efficient then it will make more money, if not, then it can choose whether to continue to offer its product as it now does or make adjustments. But Medicare advantage programs have been more expensive and not delivered better health outcomes than traditional medicare, so they are being phased out.

There are several online sources for looking at the numbers. Here is one from Oct 2010
http://www.americanprogress.org/issu...aca_report.pdf

The often mentioned Congressional Budget Office report issued in the spring 2012 is here
CBO | CBO Releases Updated Estimates for the Insurance Coverage Provisions of the Affordable Care Act

Here is the money line from their most recent report
"CBO and JCT (Joint committee on taxation) have previously estimated that the ACA will, on net, reduce budget deficits over the 2012-2021 period; that estimate of the overall budgetary impact of the ACA has not been updated."

In other words, this program will SAVE the government money if it goes according to the non-partisan CBO's analysis. This does not mean we won't be spending a lot of money, just that with the ACA we are going to spend less than we would without it (and provide tens of millions of Americans coverage they otherwise would not have)