XML 70 R58.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Intangible Assets - Carrying Amount of Goodwill Allocated by Domestic and Foreign Operations (Detail) - USD ($) $ in Millions | Mar. 31, 2018 | Dec. 31, 2017
--- | --- | ---
Goodwill [Line Items] |  |  |
Total goodwill - net | $ 4,236.3 | $ 4,164.8 | [1]
Unites States [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 2,341.0 | 2,306.7 |
United Kingdom [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 783.6 | 745.7 |
Canada [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 367.8 | 374.0 |
Australia [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 414.1 | 416.6 |
New Zealand [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 224.9 | 218.9 |
Other Foreign [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 104.9 | 102.9 |
Brokerage [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 4,189.8 | 4,119.2 |
Brokerage [Member] | Unites States [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 2,315.9 | 2,280.9 |
Brokerage [Member] | United Kingdom [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 776.0 | 738.5 |
Brokerage [Member] | Canada [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 367.8 | 374.0 |
Brokerage [Member] | Australia [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 414.1 | 416.6 |
Brokerage [Member] | New Zealand [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 214.0 | 209.3 |
Brokerage [Member] | Other Foreign [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 102.0 | 99.9 |
Risk Management [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 43.6 | 42.6 |
Risk Management [Member] | Unites States [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 25.1 | 25.8 |
Risk Management [Member] | United Kingdom [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 7.6 | 7.2 |
Risk Management [Member] | New Zealand [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 10.9 | 9.6 |
Corporate [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | 2.9 | 3.0 |
Corporate [Member] | Other Foreign [Member] |  |  |
Goodwill [Line Items] |  |  |
Total goodwill - net | $ 2.9 | $ 3.0 |
[1] | See Note 3 - Revenues from Contracts with Customers for additional information about the restatements related to ASC 606.

X
- Definition Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=35741047&loc=d3e13816-109267 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6388280&loc=d3e13770-109266 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 350 -SubTopic 20 -Section 45 -Paragraph 5 -URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975 + Details
Name: | us-gaap_Goodwill
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_GoodwillLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | us-gaap_StatementGeographicalAxis=country_US
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=country_GB
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=country_CA
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=country_AU
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=country_NZ
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementGeographicalAxis=ajg_OtherForeignMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=ajg_BrokerageSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=ajg_RiskManagementSegmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementBusinessSegmentsAxis=us-gaap_CorporateMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |