Intangible Assets (Tables)

12 Months Ended

Dec. 31, 2016

Goodwill and Intangible Assets Disclosure [Abstract]

Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations

The carrying amount of goodwill at December 31, 2016 and 2015 allocated by domestic and foreign operations is as follows (in millions):

	Brokerage		Risk Management Services Management		Corporate		Total
At December 31, 2016
United States	$	2,115.0	$	23.5	$	—	$	2,138.5
United Kingdom		662.2		4.3		—		666.5
Canada		292.2		—		—		292.2
Australia		382.7		—		—		382.7
New Zealand		205.0		0.3		—		205.3
Other foreign		79.8		—		2.8		82.6
Total goodwill - net	$	3,736.9	$	28.1	$	2.8	$	3,767.8
At December 31, 2015
United States	$	1,946.9	$	23.5	$	—	$	1,970.4
United Kingdom		779.3		3.5		—		782.8
Canada		282.6		—		—		282.6
Australia		380.1		—		—		380.1
New Zealand		204.2		0.3		—		204.5
Other foreign		42.5		—		—		42.5
Total goodwill - net	$	3,635.6	$	27.3	$	—	$	3,662.9

Changes in Carrying Amount of Goodwill

The changes in the carrying amount of goodwill for 2016 and 2015 are as follows (in millions):

	Brokerage			Risk Management Services Management			Corporate		Total
Balance as of January 1, 2015	$	3,427.5		$	22.1		$	—	$	3,449.6
Goodwill acquired during the year		352.6			2.0			—		354.6
Goodwill related to transfers of operations between segments		(3.4	)		3.4			—		—
Goodwill adjustments related to appraisals and other acquisition adjustments		25.3			—			—		25.3
Foreign currency translation adjustments during the year		(166.4	)		(0.2	)		—		(166.6	)
Balance as of December 31, 2015		3,635.6			27.3			—		3,662.9
Goodwill acquired during the year		222.6			—			2.8		225.4
Goodwill adjustments related to appraisals and other acquisition adjustments		1.8			1.6			—		3.4
Foreign currency translation adjustments during the year		(123.1	)		(0.8	)		—		(123.9	)
Balance as of December 31, 2016	$	3,736.9		$	28.1		$	2.8	$	3,767.8

Major Classes of Amortizable Intangible Assets

Major classes of amortizable intangible assets consist of the following (in millions):

	December 31,
	2016			2015
Expiration lists	$	2,757.6		$	2,613.3
Accumulated amortization - expiration lists		(1,143.0	)		(934.7	)
		1,614.6			1,678.6
Non-compete agreements		49.3			43.7
Accumulated amortization - non-compete agreements		(42.1	)		(34.8	)
		7.2			8.9
Trade names		24.0			25.7
Accumulated amortization - trade names		(18.5	)		(14.4	)
		5.5			11.3
Net amortizable assets	$	1,627.3		$	1,698.8

Estimated Aggregate Amortization Expense

Estimated aggregate amortization expense for each of the next five years is as follows (in millions):

2017	$	239.6
2018		226.8
2019		213.1
2020		197.0
2021		174.5
Total	$	1,051.0