I had an inquiry about this and am posting my response
Some relatively good news on this. The volume of over-the-counter derivatives, including Credit Default Swaps, has generally been declining since the Global Financial Crisis. It’s still large and a potential source of danger. The place to go for detailed information is the Bank of International Settlements. Here’s a press release from late 2017 with a graph for the declinehttps://www.bis.org/publ/otc_hy1711.htmI’ve attached detailed statistical data.
I suspect, though, that the real problem this time will be in more standard forms of corporate debt. The long period of low rates has allowed corporations to load up on debt. This story from Forbes is useful
And you can get statistical data for the US from the St Louis Fed