In a development that is sending ripples throughout the corporate-bond market, Verizon Communications is expected to raise $20 billion or more Wednesday in what would be the largest-ever debt sale by a company.

The New York telecommunications company will sell debt ranging in maturity from three to 30 years, the banks backing the deal said on Monday. The deal would help fund Verizon's $130 billion buyout of US wireless joint-venture partner Vodafone.