It’s no surprise that the House Republicans’ tax bill includes the eventual repeal of the estate tax, a long-held GOP goal. But The Washington Post’s Glenn Kessler highlights an unexpectedly generous aspect of the current bill: It “allows the beneficiaries of estates to not pay capital gains taxes on the increase in value of assets held by the estates. That has not been a feature of most previous estate-tax bills.”

Currently, estates face a federal tax if they’re valued at more than $5.49 million for individuals or almost $11 million for couples. But, for tax purposes, the value of assets passed on to heirs gets “stepped-up” or reset to their value at the time of death. Kessler’s example: “Imagine a home that had been purchased for $250,000 but was now worth $1 million. The ‘stepped-up basis’ would be $1 million. If the heirs sold the house for $1.1 million, they would only owe capital-gains tax on the $100,000 difference, not the $850,000 difference from the original purchase price.”

The GOP bill repeals the estate tax, but also keeps the stepped-up basis — a seemingly small detail that creates a huge tax shelter. It means that heirs of large estates would save tens of billions of dollars a year when they sell assets that have appreciated in value over time — or, as Kessler puts it, that the bill will allow “tens of billions of untapped capital gains to remain beyond the reach of the U.S. government.”