How do we pay for single payer?

From David Himmstein’s testimony before the US House:

single payer reform would make care affordable through vast savings on bureaucracy and profits. As my colleagues and I have shown in research published in the New England Journal of Medicine, administration consumes 31% of health spending in the U.S., nearly double what Canada spends. In other words, if we cut our bureaucratic costs to Canadian levels, we’d save nearly $400 billion annually — more than enough to cover the uninsured and to eliminate copayments and deductibles for all Americans. By simplifying its payment system Canada has cut insurance overhead to 1% of premiums — one twentieth of Aetna’s overhead - and eliminated mounds of expensive paperwork for doctors and hospitals. In fact, while cutting insurance overhead could save us $131 billion annually, our insurers waste much more than that because of the useless paperwork they inflict on doctors and hospitals.