Private equity firms are ready to pounce in 2020, armed with a record level of cash. Firms led by Blackstone Group Inc. and Carlyle Group LP have amassed almost $1.5 trillion in unspent capital, the highest year-end total on record, according to data compiled by Preqin. While last year saw roughly $450 billion worth of private equity deals, M&A activity this year could be on a scale not seen since the financial crisis.