How did the Bail-In in Cyprus Work?
Apparently it's deposit accounts, which I think means both savings and checking accounts. 

No, brokerage accounts are definitely not it, as they do not represent a liability for the bank. The issue is that the 'bail-in" is a reduction in the debt the bank has towards its depositors. When you own 100 of deposits, it's the bank that owes you, but when you owe a brokerage account that owns 100 of stocks, the bank owes you nothing. So, you received a statement from the bank saying you had 200000 euros in your account, then they impose a 40% levy on the uninsured part (100000). So next month you receive a bank statement that says you have now have 160000 in your account...