Two of the biggest cable companies in the United States have agreed to merge, marking a major milestone in consolidation as cord-cutters continue to ditch their pricey TV packages, thus forcing companies to adjust to their dwindling futures. Charter Communications, which operates under the Spectrum branding, is combining with its privately held rival Cox Communications, which it values at $34.5 billion including debt, the two companies announced Friday. A combined entity will help both companies compete against wireless services and improve their offerings. The combined company will be called Cox Communications, but Spectrum will be the consumer-facing name. The transaction is contingent on regulatory approval.