Employee Benefits (Tables)

9 Months Ended

Sep. 30, 2017

Retirement Benefits [Abstract]

Components of net periodic benefit cost for the pension plans

The following table provides the components of the net periodic cost (benefit) recognized in the Condensed Consolidated Statements of Income in Compensation and benefits for Aon’s material U.K., U.S., and other significant international pension plans located in the Netherlands and Canada (in millions):

	Three months ended September 30
	U.K.						U.S.						Other
	2017			2016			2017			2016			2017			2016
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	31			37			24			28			7			7
Expected return on plan assets, net of administration expenses	(50		)	(58		)	(34		)	(39		)	(13		)	(12		)
Amortization of prior-service cost	—			—			—			1			—			—
Amortization of net actuarial loss	8			7			13			12			3			3
Net periodic cost (benefit)	$	(11	)	$	(14	)	$	3		$	2		$	(3	)	$	(2	)
Loss on pension settlement	—			—			—			—			—			—
Total net periodic cost (benefit)	$	(11	)	$	(14	)	$	3		$	2		$	(3	)	$	(2	)
	Nine months ended September 30
	U.K.						U.S.						Other
	2017			2016			2017			2016			2017			2016
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	91			123			72			83			19			21
Expected return on plan assets, net of administration expenses	(147		)	(187		)	(104		)	(117		)	(35		)	(36		)
Amortization of prior-service cost	—			1			1			2			—			—
Amortization of net actuarial loss	23			24			38			37			9			8
Net periodic cost (benefit)	$	(33	)	$	(39	)	$	7		$	5		$	(7	)	$	(7	)
Loss on pension settlement	—			61			—			—			—			—
Total net periodic cost (benefit)	$	(33	)	$	22		$	7		$	5		$	(7	)	$	(7	)