Employee Benefits (Tables)

9 Months Ended

Sep. 30, 2018

Retirement Benefits [Abstract]

Components of net periodic benefit cost for the pension plans

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

	Three months ended September 30
	U.K.						U.S.						Other
	2018			2017			2018			2017			2018			2017
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	26			31			24			24			6			7
Expected return on plan assets, net of administration expenses	(46		)	(50		)	(36		)	(34		)	(11		)	(13		)
Amortization of prior-service cost	1			—			—			—			—			—
Amortization of net actuarial loss	6			8			15			13			3			3
Net periodic (benefit) cost	(13		)	(11		)	3			3			(2		)	(3		)
Loss on pension settlement	9			—			—			—			—			—
Total net periodic (benefit) cost	$	(4	)	$	(11	)	$	3		$	3		$	(2	)	$	(3	)

	Nine months ended September 30
	U.K.						U.S.						Other
	2018			2017			2018			2017			2018			2017
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	84			91			74			72			20			19
Expected return on plan assets, net of administration expenses	(147		)	(147		)	(108		)	(104		)	(34		)	(35		)
Amortization of prior-service cost	1			—			1			1			—			—
Amortization of net actuarial loss	21			23			45			38			9			9
Net periodic (benefit) cost	(41		)	(33		)	12			7			(5		)	(7		)
Loss on pension settlement	32			—			—			—			—			—
Total net periodic (benefit) cost	$	(9	)	$	(33	)	$	12		$	7		$	(5	)	$	(7	)