It represents the first disposal of government assets in the rescue of GM's GMAC, a provider of financing to auto customers which expanded to include insurance, online banking, mortgage operations and commercial finance.

Hit hard in the financial crisis, sparked by a collapse of the home loan industry, GMAC was bailed out by the government, receiving $16.3 billion in taxpayer-funded aid in installments beginning in December 2008.

It was renamed Ally Financial in 2010.

The offering of Ally preferred shares is being led by Citigroup, Deutsche Bank, JP Morgan and Morgan Stanley, the Treasury said in a statement.

It did not say when the sale would take place.

"All proceeds raised from this first sale would represent a partial recovery on Treasury's investment in Ally," the department said.

The Treasury said the sale would leave unchanged its 74 percent holding of Ally common shares.

Ally is expected to make an initial public offering on the stock market of its common shares, valued last December at an estimated $23 billion, but has not yet released a date.