| Cover | Feb. 04, 2022 |
| Document Information [Line Items] | |
| Document Type | 8-K |
| Document Period End Date | Feb. 4, 2022 |
| Entity Registrant Name | Aon plc |
| Entity Incorporation, State or Country Code | L2 |
| Entity File Number | 1-7933 |
| Entity Tax Identification Number | 98-1539969 |
| Entity Address, Address Line One | Metropolitan Building |
| Entity Address, Address Line Two | James Joyce Street |
| Entity Address, City or Town | Dublin 1 |
| Entity Address, Country | IE |
| Entity Address, Postal Zip Code | D01 K0Y8 |
| City Area Code | 353 1 |
| Local Phone Number | 266 6000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Amendment Flag | false |
| Entity Central Index Key | 0000315293 |
| Class A Ordinary Shares $0.01 nominal value | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Class A Ordinary Shares $0.01 nominal value |
| Trading Symbol | AON |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 4.000 Senior Notes Due 2023 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 4.000% Senior Notes due 2023 |
| Trading Symbol | AON23 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 3.500 Senior Notes Due 2024 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 3.500% Senior Notes due 2024 |
| Trading Symbol | AON24 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 3.875 Senior Notes Due 2025 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 3.875% Senior Notes due 2025 |
| Trading Symbol | AON25 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 3.875 Senior Notes Due 2026 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 3.875% Senior Notes due 2026 |
| Trading Symbol | AON 26 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 2.05 Senior Notes Due 2031 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc's 2.050% Senior Notes due 2031 |
| Trading Symbol | AON31 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plc’s 2.60% Senior Notes Due 2031 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc's 2.600% Senior Notes due 2031 |
| Trading Symbol | AON31A |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 2.875 Senior Notes Due 2026 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 2.875% Senior Notes due 2026 |
| Trading Symbol | AON26 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 4.250 Senior Notes Due 2042 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 4.250% Senior Notes due 2042 |
| Trading Symbol | AON42 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 4.450 Senior Notes Due 2043 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 4.450% Senior Notes due 2043 |
| Trading Symbol | AON43 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 4.600 Senior Notes Due 2044 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 4.600% Senior Notes due 2044 |
| Trading Symbol | AON44 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 4.750 Senior Notes Due 2045 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 4.750% Senior Notes due 2045 |
| Trading Symbol | AON45 |
| Security Exchange Name | NYSE |
| Guarantees Of Aon Plcs 2.90 Senior Notes Due 2051 | |
| Document Information [Line Items] | |
| Title of 12(b) Security | Guarantees of Aon plc’s 2.900% Senior Notes due 2045 |
| Trading Symbol | AON51 |
| Security Exchange Name | NYSE |
