+1 -- Plenty of fares that book into A are refundable it just depends on the underlying fare (recall that there are no A fares just economy fares that book into A inventory as instant upgrades).

To the OP, assuming you have a fully refundable fare, you can get an idea of the value of each segment by looking at the fare calculation line included in your Flight Receipt. This is the somewhat cryptic data included after the more readable details in the receipt right above the "Checked Bag Allowance" heading in the typical emailed receipt.

Here is an example from a recent trip I took from ATL-CMH-MSP.

ATL DL CMH774.88Y0 DL MSP570.23SA0RA0MQ USD1345.11END ZP ATLCMH XF ATL4.5CMH4.5

The RED section is the ATL-CMH component. The value is $774.88 and the fare code is Y0. The Blue section is the CMH-MSP component and the value is $570.23 and the fare code is SA0RA0MQ. Since both fares are refundable (based on a review of the fare rules) and they each fared separately and have no other restrictions I could cancel the CMH-MSP segment and get a refund of $570.23 plus tax.

If this was fared as ATL-MSP with a stop in CMH then the above described refund would not be possible without refaring the ticket. Domestically DL has a lot of refundable unrestricted fares (not just Y) however internationally there is a lot less flexibility (i.e. more refundable but restricted fares) and some fares are refundable but still have a change fee (e.g. fully refundable minus a change fee of $400). Here is an example of a fare from MSP-MQT with a stop in DTW:

MSP DL X/DTT DL MQT670.70Y0 DL X/DTT DL MSP670.70Y0 USD1341.40END ZP MSPDTW0MQT0DTW XF MSP4.5DTW4.5MQT4.5DTW4.5

Note the difference here that the fare is MSP-MQT for $670.70 (red above) and MQT-MSP (blue above) and that MSP-DTW and DTW-MQT are not fared separately and therefore not individually refundable. A notation of X/[Airport] indicates the connection point that is not a fare break (note that DTT is the city code for Detroit and includes all area airports with DTW being the biggest). If you wanted to stop in DTW then DL would have to reprice it based on MSP-DTW fare and the refund (or collection) would be based on that new fare.

If you post the full fare rules here for all coupons (segments) included in your ticket I am sure the we can help figure it out however your best bet is to just call Delta and ask.