Employee Benefits (Tables)

6 Months Ended

Jun. 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 cost (benefit) 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 June 30
	U.K.						U.S.						Other
	2018			2017			2018			2017			2018			2017
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	29			30			25			24			7			6
Expected return on plan assets, net of administration expenses	(50		)	(49		)	(36		)	(35		)	(11		)	(11		)
Amortization of prior-service cost	—			—			1			1			—			—
Amortization of net actuarial loss	7			8			15			12			3			3
Net periodic cost (benefit)	(14		)	(11		)	5			2			(1		)	(2		)
Loss on pension settlement	16			—			—			—			—			—
Total net periodic cost (benefit)	$	2		$	(11	)	$	5		$	2		$	(1	)	$	(2	)

	Six months ended June 30
	U.K.						U.S.						Other
	2018			2017			2018			2017			2018			2017
Service cost	$	—		$	—		$	—		$	—		$	—		$	—
Interest cost	58			60			50			48			14			12
Expected return on plan assets, net of administration expenses	(101		)	(97		)	(72		)	(70		)	(23		)	(22		)
Amortization of prior-service cost	—			—			1			1			—			—
Amortization of net actuarial loss	15			15			30			25			6			6
Net periodic cost (benefit)	(28		)	(22		)	9			4			(3		)	(4		)
Loss on pension settlement	23			—			—			—			—			—
Total net periodic cost (benefit)	$	(5	)	$	(22	)	$	9		$	4		$	(3	)	$	(4	)