Cover Page - shares	6 Months Ended
	Jun. 30, 2019	Jul. 25, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Jun. 30, 2019
Document Transition Report	false
Entity File Number	1-7933
Entity Registrant Name	Aon plc
Entity Incorporation, State or Country Code	X0
Entity Tax Identification Number	98-1030901
Entity Address, Address Line One	122 LEADENHALL STREET
Entity Address, City or Town	LONDON
Entity Address, Country	GB
Entity Address, Postal Zip Code	EC3V 4AN
City Area Code	20
Local Phone Number	7623 5500
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		235,841,886
Entity Central Index Key	0000315293
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q2