Updated Tuesday, Dec. 18

WASHINGTON — The Senate passed a bipartisan bill on Tuesday to change federal prison and sentencing laws, putting the nation on the brink of its most sweeping overhaul of the federal corrections system in decades.

The proposal would allow for shorter prison terms and more judicial discretion in sentencing, unwinding some of the tough-on-crime policies that have swelled the federal prison population. But revisions in the latest version narrow the categories of inmates who could benefit from new incentives to shave prison terms.

Here is some of what the legislation, called the First Step Act, would do:

Federal judges would have more discretion to bypass mandatory minimums and lighten drug sentences.

This would have a significant effect on African-Americans, who have faced much higher incarceration rates for drug crimes than white offenders.

Under the new guidelines, the mandatory minimum sentence for serious violent crimes or serious drug offenses would be reduced to 15 years from 20 years.