These were two separate sources of cash/assets. There was the $4B cash in a demand deposit that belonged to WMI that was eventually returned and used to pay the $7B Creditor debt.
Then there was the $4B in Trust Preferred Securities (TPS) that were backed by assets. What I'm not sure about is what exactly was transferred back to WMI in the Exchange Event.
From the POR it was shown that JPM is the sole equitable and beneficial owner of the TPS. It is possible that a deal was reached where WMI got the $4B cash and JPM got the $4B in TPS.
If the latter was the case then IMO that was one of the worst deals ever negotiated. Both seemed to be clearly the property of WMI.
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