Accelerating Aon United Program - Restructuring Liabilities for the Program (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2025	Dec. 31, 2024	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Charges	$ 365	$ 389	$ 135
Accelerating Aon United Program
Restructuring Reserve [Roll Forward]
Liability balance as of December 31, 2024	114
Charges	365	389
Cash payments	(297)
Foreign currency translation and other	6
Non-cash charges	(41)
Liability balance as of December 31, 2025	147	114
Total costs incurred from inception to date	889
Accelerating Aon United Program | Technology and other
Restructuring Reserve [Roll Forward]
Liability balance as of December 31, 2024	17
Charges	195
Cash payments	(165)
Foreign currency translation and other	0
Non-cash charges	(8)
Liability balance as of December 31, 2025	39	17
Total costs incurred from inception to date	335
Accelerating Aon United Program | Workforce optimization
Restructuring Reserve [Roll Forward]
Liability balance as of December 31, 2024	97
Charges	155
Cash payments	(132)
Foreign currency translation and other	6
Non-cash charges	(18)
Liability balance as of December 31, 2025	108	97
Total costs incurred from inception to date	455
Accelerating Aon United Program | Asset impairments
Restructuring Reserve [Roll Forward]
Liability balance as of December 31, 2024	0
Charges	15
Cash payments	0
Foreign currency translation and other	0
Non-cash charges	(15)
Liability balance as of December 31, 2025	0	$ 0
Total costs incurred from inception to date	$ 99