While the current cycle of declining interest rates has been running for at least 25 years, the most recent iteration of the period has been exceptionally benign. Since the end of the global financial crisis, corporate and, to a greater extent government, borrowing costs have run at the levels close to, or even below, those observed in the 1950s-1960s.
Since 2002-2003, FFR, on average, has been below the risk premium on lending to the government and corporates. This has changed in 4Q 2017 when Treasuries' risk premium fell below the FFR and stayed there since.