Aon vs Marsh & Mclennan Companies (AON vs MRSH)
Side by side from their SEC filings: revenue, margins, growth, returns and valuation, plus short interest, insider activity and institutional ownership.
Marsh & Mclennan Companies is the larger company by revenue ($27.0B vs $17.2B) and market value ($86.0B vs $77.3B). Aon has grown revenue faster over the last 4 fiscal years (+40.9% cumulative vs +36.1%). Aon runs the higher operating margin (25.3% vs 23.1%). Aon trades at the lower trailing P/E (19.5x vs 22.3x).
About Aon
Aon plc is a global professional services firm that provides risk management, insurance brokerage, reinsurance, and human capital consulting services. Its main business segments are Risk Capital, which offers insurance and reinsurance brokerage and consulting, and Human Capital, which delivers health, benefits, talent advisory, and retirement consulting services. Aon serves clients in over 120 countries across various industries and market segments.
About Marsh & Mclennan Companies
Marsh & McLennan Companies, Inc. provides risk management, insurance and reinsurance brokerage, and consulting services worldwide. Its Risk and Insurance Services segment includes Marsh Risk, which offers insurance broking, risk advisory, and program management, and Guy Carpenter, which specializes in reinsurance broking and strategic advisory. The Consulting segment delivers health, wealth, career advice, and management consulting services through Mercer and Marsh Management Consulting to organizations globally.
Head to head (AON FY2025 vs MRSH FY2025)
| Metric | AONFY2025 | MRSHFY2025 |
|---|---|---|
| Revenue | $17.18B | $26.98B |
| Revenue growth (YoY) | 9.4% | 10.3% |
| Gross margin | — | — |
| Operating margin | 25.3% | 23.1% |
| Net margin | 21.5% | 15.4% |
| Net income | $3.69B | $4.16B |
| Diluted EPS | $17.02 | $8.43 |
| FCF margin | 18.7% | 18.5% |
| ROE | 39.1% | 27.2% |
| Debt / equity | 1.5× | 1.2× |
| Market cap | $77.25B | $86.02B |
| P/E (TTM) | 19.5× | 22.3× |
Fundamentals are from each company’s SEC filings (AON FY2025, MRSH FY2025). P/E and market cap are derived from recent market prices and update daily.
Five-year trend (as reported)
| Revenue | FY2021 | FY2022 | FY2023 | FY2024 | FY2025 |
|---|---|---|---|---|---|
| AON | $12.19B | $12.48B | $13.38B | $15.70B | $17.18B |
| MRSH | $19.82B | $20.72B | $22.74B | $24.46B | $26.98B |
Peer standing
Where each company ranks among the 88 insurance companies, on the same scale. Each figure is ranked only against peers that report it. Percentiles describe position in the distribution, not a rating.
| Metric | AON | MRSH |
|---|---|---|
| Operating margin | 25.3%85th percentile of 27 | 23.1%77th percentile of 27 |
| Net margin | 21.5%83rd percentile of 82 | 15.4%69th percentile of 82 |
| FCF margin | 18.7%59th percentile of 55 | 18.5%57th percentile of 55 |
| Revenue growth (YoY) | +9.4%49th percentile of 88 | +10.3%54th percentile of 88 |
| ROE | 39.1%99th percentile of 73 | 27.2%83rd percentile of 73 |
| P/E (TTM) | 19.5×77th percentile of 71 | 22.3×83rd percentile of 71 |
| Debt / equity | 1.55×94th percentile of 48 | 1.20×87th percentile of 48 |
| Short interest (days to cover) | 4.04d48th percentile of 86 | 2.08d15th percentile of 86 |
Short interest
| FINRA settlement data | AON | MRSH |
|---|---|---|
| Shares sold short | 4.6M | 5.0M |
| Change vs prior settlement | +23.2% | -5.2% |
| Days to cover | 4.04 | 2.08 |
| As of settlement | 2026-07-15 | 2025-12-31 |
Source: FINRA Consolidated Short Interest. FINRA is the owner and source of the FINRA-supplied data; republishing or redistributing it is not permitted. Not presented as a percentage of float. No FINRA endorsement of this product is implied.
Insider activity (last 90 days)
| Form 4 open-market activity | AON | MRSH |
|---|---|---|
| Buys | 0 | 0 |
| Sells | 4 ($941,500) | 2 ($4.8M) |
Open-market purchases and sales reported on SEC Form 4 (grants, exercises and tax withholding excluded). For context, about 16% of covered companies saw any open-market insider buy in a 90-day window.
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Data sourced from SEC EDGAR (public domain). Figures are as-reported and may be unaudited or restated; verify against the source filings before relying on them. Comparisons are descriptive (higher or lower on a reported figure), not a rating or a recommendation. Informational only. Not investment advice.