Exhibit 12.1

Aon Corporation and Consolidated Subsidiaries

Combined With Unconsolidated Subsidiaries

Computation of Ratio of Earnings to Fixed Charges

|  | Nine Months ended |  |  |  |  |  |  |  |  |  |  |
|  | September 30, |  | Years Ended December 31, |
(millions except ratio) |  | 2011 |  | 2010 |  | 2010 |  | 2009 |  | 2008 |  | 2007 |  | 2006 |
Income from continuing operations before income taxes and noncontrolling interests |  | $ | 1,000 |  | $ | 699 |  | $ | 1,059 |  | $ | 949 |  | $ | 879 |  | $ | 1,023 |  | $ | 738 |
Less: Equity in earnings on less than 50% owned entities |  | (7 | ) | 3 |  | 10 |  | 11 |  | 5 |  | 6 |  | 5 |
Add back fixed charges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest on indebtedness |  | 186 |  | 117 |  | 182 |  | 122 |  | 126 |  | 138 |  | 129 |
Interest on uncertain tax positions |  | 1 |  | 1 |  | (1 | ) | 2 |  | — |  | 2 |  | — |
Portion of rents representative of interest factor |  | 37 |  | 29 |  | 48 |  | 48 |  | 47 |  | 75 |  | 79 |
Income as adjusted |  | $ | 1,231 |  | $ | 843 |  | $ | 1,278 |  | $ | 1,110 |  | $ | 1,047 |  | $ | 1,232 |  | $ | 941 |
Fixed charges: |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest on indebtedness |  | $ | 186 |  | $ | 117 |  | $ | 182 |  | $ | 122 |  | $ | 126 |  | $ | 138 |  | $ | 129 |
Interest on uncertain tax positions |  | 1 |  | 1 |  | (1 | ) | 2 |  | — |  | 2 |  | — |
Portion of rents representative of interest factor |  | 37 |  | 29 |  | 48 |  | 48 |  | 47 |  | 75 |  | 79 |
Total fixed charges |  | $ | 224 |  | $ | 147 |  | $ | 229 |  | $ | 172 |  | $ | 173 |  | $ | 215 |  | $ | 208 |
Ratio of earnings to fixed charges |  | 5.5 |  | 5.7 |  | 5.6 |  | 6.5 |  | 6.1 |  | 5.7 |  | 4.5 |