Kelly Cloonan

Shares of General Motors fell, even after the automaker approved a new $20 billion buyback program and better third-quarter results than Wall Street was expecting.

The stock declined 6.9% to $77.01 in premarket trading on Tuesday. At Monday's market close, shares were up 1.8% year to date.

The company said the authorization allows it to buy back shares at any time. GM has repurchased nearly $30 billion in shares in the last five years.

For the third quarter, GM reported adjusted earnings per share of $3.70, just ahead of analyst estimates of $3.69, according to FactSet.

Revenue rose 2.9% to $50.02 billion, above analyst estimates of $48.78 billion.

GM also narrowed its outlook from July.

Chief Executive Mary Barra said GM is navigating growing inflationary pressures. The company is working to offset the headwinds with strategic investments in new products and services, she said, and expects its portfolio to get stronger in the next several years with the launches of several new models.

"We think this is a proven strategy," Barra said in a letter to shareholders.