Accelerating Aon United Program - Schedule of Changes in the Company’s Liabilities for the Program (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Restructuring Reserve [Roll Forward]
Charges	$ 132	$ 0	$ 251	$ 0
Accelerating Aon United Program
Restructuring Reserve [Roll Forward]
Liability balance as of January 1, 2024			100
Charges	132		251
Cash payments			(98)
Foreign currency translation and other			(3)
Non-cash charges			(92)
Liability balance as of June 30, 2024	158		158
Total costs incurred from inception to date	386		386
Asset amortization	12		20
Accelerating Aon United Program | Technology and other
Restructuring Reserve [Roll Forward]
Liability balance as of January 1, 2024			14
Charges			51
Cash payments			(29)
Foreign currency translation and other			0
Non-cash charges			(27)
Liability balance as of June 30, 2024	9		9
Total costs incurred from inception to date	65		65
Accelerating Aon United Program | Workforce optimization
Restructuring Reserve [Roll Forward]
Liability balance as of January 1, 2024			86
Charges			145
Cash payments			(69)
Foreign currency translation and other			(3)
Non-cash charges			(10)
Liability balance as of June 30, 2024	149		149
Total costs incurred from inception to date	248		248
Accelerating Aon United Program | Asset impairments
Restructuring Reserve [Roll Forward]
Liability balance as of January 1, 2024			0
Charges			55
Cash payments			0
Foreign currency translation and other			0
Non-cash charges			(55)
Liability balance as of June 30, 2024	0		0
Total costs incurred from inception to date	$ 73		$ 73