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Marsh & McLennan Companies, Inc., doing business as Marsh McLennan and Marsh, is an American professional services firm headquartered in New York City, with businesses in insurance brokerage, risk management, reinsurance services, talent management, investment advisory, and management consulting. Its four main operating companies are Marsh (54% of 2025 revenues), which offers risk management, insurance broking, insurance program management, risk consulting, analytical modeling, and alternative risk financing services; Marsh Re (formerly Guy Carpenter; 10% of 2025 revenues), a reinsurance intermediary and advisor; Mercer (23% of 2025 revenues), which provides consulting to employers for health insurance, retirement plans, and pension plans; and Oliver Wyman (13% of 2025 revenues), including Lippincott and NERA Economic Consulting, which provides consulting services.