security dump-keychain -d
Online manpages can be outdated or incomplete. Check the command itself:

$ security help dump-keychain

Usage: dump-keychain [-adir] [keychain...]
    -a  Dump access control list of items
    -d  Dump (decrypted) data of items
    -i  Interactive access control list editing mode
    -r  Dump the raw (encrypted) data of items