As this debt comes due, many companies will need to find new funding to replace the maturing debt.
The rating agency estimated scheduled maturities will rise to $1.93 trillion in 2017 and reach a peak maturity in 2020, when $2.09 trillion comes due.
It noted that of the total debt maturing through 2020, 24 per cent is speculative grade, and this debt is relatively higher risk, with a greater potential to experience refinancing stress.
"While funding conditions in recent years have been very favourable for corporate issuers, we believe funding conditions currently are tightening in response to falling commodity prices and volatile markets," it said.