Originally Posted by CVG_Kid

Amex and Discover own their transaction networks and act as both the card issuer and the merchant bank. That's why they can see your transaction detail.

Visa and Mastercard do not own their transaction networks. They have contracts with their merchant banks. When you dispute a charge a request is placed through the MasterCom system to request a copy of your charge detail. MasterCom's rules require a reason code within contract stipulations be provided to turn over this information which is stored at the merchant bank level. A code exists for Fraud but MS does not meet that criteria and exposes the issuers to sanction and legal recourse if they request charge detail outside the contract parameters.

There is a lot of chatter about Level 2 and 3 data from the merchants but I've never heard of this used for charge detail outside of certain merchant codes like hotels and airlines which may pass your itinerary to the issuer.