pre_text: Stock options weighted average remaining contractual terms (in years) information at December 31, for the years 2019, 2018, and 2017 is as follows: As of December 31, 2019, total unrecognized expense related to non-vested restricted stock unit awards and stock options was $45 million, and is expected to be recognized over a weighted average period of 1.8 years.
table: 2019 2018 2017
table: Outstanding 4.2 3.6 4.1
table: Vested and expected to vest 5.0 3.6 4.1
table: Exercisable 2.1 2.4 2.8
question: Analyse this data from a financial earnings document. What was the change in the Exercisable amount in 2019 from 2018?