I have a section under my employers where I list any notable accomplishments. In theory you could list that statistic there.
However, unless you can enumerate the savings in terms of real cost then listing it on a resume is not very useful.
Some related metrics that might be useful:
- Improved performance Benchmarks
- Reduced actual costs of operation
- Reduced actual costs of development
- Reduced actual costs of on going maintenance.
However for these, as a prospective employer I am going to want to to be able to explain and talk about how you came by your metrics. You need to be able to speak with confidence about them and understand those numbers inside out. If you can not do that Unless you have some documentation to back up the numbers I would leave them off. A generic "significant improvement in X," suffices.
Lean Metrics is a good way of coming by these numbers. However it requires planning ahead to capture the before and after numbers. It is hard to establish good numbers for a resume after you have left a position. So it is important if you wish to include them in your resume that you capture them regularly. Fortunately they are also useful in business so you manager will probably thank you for producing the numbers for him.