Not sure you necessarily need dc. If you wanted count of unique combinations using the 5 fields you listed:
index=main auditSource=filing auditType=FilingCompleted OR auditType=FilingSubmissionAcknowledged | stats count by "detail.Filing ID", field1, field2, field3, field4 | table field1, field2, field3, field4
However, if you really only want to use "detail.Filing ID" to remove duplicates:
index=main auditSource=filing auditType=FilingCompleted OR auditType=FilingSubmissionAcknowledged | stats latest(*) AS * by "detail.Filing ID" | table field1, field2, field3, field4
You can substitute latest for earliest, first, or last, depending on if you want the first matching field or the last, or you want the earliest chronologically matching field or the latest.
http://docs.splunk.com/Documentation/Splunk/6.3.3/SearchReference/CommonStatsFunctions
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