John Cochrane points to this from the Richmond Fed (he has a few additional comments):
Bailout Barometer: How Large is the Financial Safety Net?: ...The Bailout Barometer is our estimate of the share of financial system liabilities for which the federal government provides protection from losses. In addition to protection from explicit government guarantee programs, our estimate includes implicit protection that people are likely to infer from past government actions and statements. Despite efforts to end ad hoc bailouts, the financial safety net that protects certain firms remains large under current government policies.
How large is it?
Our latest estimate shows that the financial safety net covers 60 percent of the financial sector. This estimate also includes a breakdown by sector. These measures, compiled in March 2015, use data as of December 31, 2013. Our Bailout Barometer has grown considerably since our first estimate in 1999.
Why does it matter?
When creditors expect to be protected from losses, they will overfund risky activities, making financial crises and bailouts like those that occurred in 2007-08 more likely. An extensive safety net also creates a need for robust supervision of firms benefitting from perceived protection. Over time, shrinking the financial safety net is essential to restore market discipline and achieve financial stability. Doing so requires credible limits on ad hoc bailouts. Read more on our perspective.
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