U.S. Strategic Nuclear Forces: Background, Developments, and Issues [Updated January 3, 2020] [open pdf - 1MB]
From the Summary: "Even though the United States has reduced the number of warheads deployed on its long-range missiles and bombers, consistent with the terms of the 2010 New START [Strategic Arms Reduction Treaty] Treaty, it is also developing new delivery systems for deployment over the next 10-30 years. The 116th Congress will continue to review these programs, and the funding requested for them, during the annual authorization and appropriations process."
CRS Report for Congress, RL33640
Congressional Research Service: https://crsreports.congress.gov/