Segment Information (Tables)

12 Months Ended

Dec. 31, 2024

Segment Reporting [Abstract]

Schedule of Reportable Operating Segments, Consolidated Revenue and Segment Operating Income

The following tables include information about our reportable segments, including total segment revenue, consolidated revenue, segment operating income, and income before income taxes:

	Year Ended December 31, 2024
(millions, except per share data)	Risk Capital			Human Capital			Corporate/Eliminations		Total Consolidated
Revenue
Total revenue (1)	$	10,517		$	5,209		$	(28)	$	15,698
Expenses
Compensation and benefits	5,417			2,739			127		8,283
Information technology	368			168			3		539
Premises	215			110			—		325
Other expenses (2)	1,225			1,049			442		2,716
Total operating expenses	7,225			4,066			572		11,863
Operating income	3,292			1,143			(600)		3,835
Operating margin	31.3		%	21.9		%			24.4		%
Non-operating expenses
Interest income									67
Interest expense									(788)
Other income (expense)									348
Income before income taxes									$	3,462

(1)Includes fiduciary investment income of $307 million in Risk Capital and $8 million in Human Capital for 2024.

(2)Includes expenses related to Depreciation of fixed assets, Amortization and impairment of intangible assets, Accelerating Aon United Program expenses, and Other general expenses.

	Year Ended December 31, 2023
(millions, except per share data)	Risk Capital			Human Capital			Corporate/Eliminations		Total Consolidated
Revenue
Total revenue (1)	$	9,524		$	3,864		$	(12)	$	13,376
Expenses
Compensation and benefits	4,800			2,003			99		6,902
Information technology	385			148			1		534
Premises	204			88			2		294
Other expense (2)	1,189			528			144		1,861
Total operating expenses	6,578			2,767			246		9,591
Operating income	2,946			1,097			(258)		3,785
Operating margin	30.9		%	28.4		%			28.3		%
Non-operating expenses
Interest income									31
Interest expense									(484)
Other income (expense)									(163)
Income before income taxes									$	3,169

(1)Includes fiduciary investment income of $270 million in Risk Capital and $4 million in Human Capital for 2023.

(2)Includes expenses related to Depreciation of fixed assets, Amortization and impairment of intangible assets, Accelerating Aon United Program expenses, and Other general expenses.

	Year Ended December 31, 2022
(millions, except per share data)	Risk Capital			Human Capital			Corporate/Eliminations		Total Consolidated
Revenue
Total revenue (1)	$	8,905		$	3,591		$	(17)	$	12,479
Expenses
Compensation and benefits	4,532			1,856			89		6,477
Information technology	361			146			2		509
Premises	195			88			6		289
Other expense (2)	922			540			73		1,535
Total operating expenses	6,010			2,630			170		8,810
Operating income	2,895			961			(187)		3,669
Operating margin	32.5		%	26.8		%			29.4		%
Non-operating expenses
Interest income									18
Interest expense									(406)
Other income (expense)									(125)
Income before income taxes									$	3,156

(1)Includes fiduciary investment income of $76 million in Risk Capital and less than $1 million in Human Capital for 2022.

(2)Includes expenses related to Depreciation of fixed assets, Amortization and impairment of intangible assets, Accelerating Aon United Program expenses, and Other general expenses.

Schedule of Geographic Areas of Fixed Assets and Operating Lease Right-of-Use Asset

The following table includes consolidated long-lived assets, net by geographic area (in millions). Long-lived assets are comprised of Fixed assets, net, Operating lease right-of-use assets, and finance lease assets classified as Other non-current assets:

As of December 31	Total		United States		Americas other than U.S.		United Kingdom		Ireland		Other Europe, Middle East, & Africa		Asia Pacific
2024	$	1,357	$	598	$	117	$	144	$	28	$	261	$	209
2023	$	1,314	$	492	$	124	$	159	$	7	$	297	$	235