This doesn't seem like a "you can totally investigate that because I've successfully swept billions of dollars in laundered money under the rug without a trace" move, it's more like a "no, seriously, don't investigate that, because then I'd be totally screwed" kinda move.
I predict that Trump will try to fire Mueller within three weeks. That should be enough time for indications that Mueller has begun looking into Trump's finances to come to light.
The other big story of the day, stemming from the same interview. When listening to the audio myself, it immediately struck me as strange that Trump equates Sessions's recusal from the Russia probe with Sessions "not doing his job". It's like helping Trump deal with the heat from Russia-related inquiries was the one thing Trump expected Sessions to do.
My apologies for continuing to post Trump-Russia content here, but I'll never quench my thirst to see this man imprisoned.
Edit: holy shit, it took less than a day for Mueller to announce that you're gooddamn right he's looking into Trump's finances.