The BlackRock logo is seen outside of its offices in New York City, U.S., October 17, 2016. REUTERS/Brendan McDermid

NEW YORK (Reuters) - BlackRock Inc’s exchange-traded fund unit, iShares, topped $1 trillion in assets in the United States for the first time, a spokeswoman said on Tuesday.

The milestone, reached last Thursday, came after a dramatic shift in markets since the November U.S. presidential election, including a rally in U.S. stocks, and is a capstone in a move by investors to lower-cost ETFs.

ETFs are a basket of stocks or other assets traded by individual investors and institutions. They often charge lower fees than many mutual funds, incur fewer taxes and offer the convenience of buying entire markets as simply as trading a single stock. Many track indexes instead of trying to beat the market.

Demand for ETFs has so far survived debate over the durability of the funds during market stress.

ETFs took in $375 billion globally in 2016. BlackRock pulled in $140 billion of that, including $105 billion in the United States, according to BlackRock and FactSet Research Systems Inc.

“We’re seeing our clients expand the use of iShares ETFs to replace individual securities, to execute more efficiently than swaps, futures or individual bonds, to take long-term core positions and to construct efficient portfolios,” Martin Small, the U.S. head of iShares, said in an emailed statement.

In 2009, BlackRock bought the iShares business from Barclays, which had helped popularize the funds. Today, iShares account for a quarter of BlackRock’s assets under management.