QuickLinks -- Click here to rapidly navigate through this document

Exhibit 99.4

AON CORPORATION
SEGMENTS AS RECLASSIFIED—EXCLUDING PREVIOUSLY REPORTED SPECIAL & UNUSUAL CHARGES

			2002
(millions)			1st Qtr.			2nd Qtr.			3rd Qtr.			4th Qtr.			Full Year
REVENUE
	Risk & Insurance Brokerage Services		$	1,157		$	1,215		$	1,247		$	1,354		$	4,973
	Consulting			233			248			269			304			1,054
	Insurance Underwriting			649			750			718			684			2,801
	Corporate & Other			49			(91	)		12			24			(6	)
		Total Revenue	$	2,088		$	2,122		$	2,246		$	2,366		$	8,822
INCOME (LOSS) BEFORE INCOME TAXES
	Risk & Insurance Brokerage Services		$	189		$	138		$	191		$	238		$	756
	Consulting			27			23			26			44			120
	Insurance Underwriting			73			5			41			44			163
	Corporate & Other			(13	)		(153	)		(59	)		(48	)		(273	)
		Total Income Before Income Taxes	$	276		$	13		$	199		$	278		$	766

AON CORPORATION
SEGMENTS AS RECLASSIFIED—EXCLUDING PREVIOUSLY REPORTED SPECIAL & UNUSUAL CHARGES

			2001
(millions)			1st Qtr.			2nd Qtr.			3rd Qtr.			4th Qtr.			Full Year
REVENUE
	Risk & Insurance Brokerage Services		$	1,052		$	1,083		$	1,030		$	1,198		$	4,363
	Consulting			212			229			232			265			938
	Insurance Underwriting			628			609			641			643			2,521
	Corporate & Other			(81	)		(4	)		9			(70	)		(146	)
		Total Revenue	$	1,811		$	1,917		$	1,912		$	2,036		$	7,676
INCOME (LOSS) BEFORE INCOME TAXES
	Risk & Insurance Brokerage Services		$	198		$	190		$	150		$	193		$	731
	Consulting			25			30			29			49			133
	Insurance Underwriting			69			83			90			85			327
	Corporate & Other			(172	)		(93	)		(83	)		(158	)		(506	)
		Total Income Before Income Taxes	$	120		$	210		$	186		$	169		$	685

QuickLinks

Exhibit 99.4