XML 72 R60.htm IDEA: XBRL DOCUMENT
v3.7.0.1

Investments - Investments Reported in Other Current and Non-Current Assets (Parenthetical) (Detail) - Clean-Coal Investments [Member] | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2017 Entity Plant | Dec. 31, 2016 Entity Plant
Fourteen 2009 Era Clean Coal Plants [Member] | Controlling Interest [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Number of coal plants | Plant | 14 | 14
Number of variable interest entities | Entity | 6 | 6
One 2011 Era Clean Coal Plant [Member] | Noncontrolling Interests [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Number of coal plants | Plant | 1 | 1
Number of variable interest entities | Entity | 1 | 1
Nineteen 2011 Era Clean Coal Plants [Member] | Controlling Interest [Member] |  |
Schedule of Equity Method Investments [Line Items] |  |
Number of coal plants | Plant | 19 | 19
Number of variable interest entities | Entity | 17 | 17

X
- Definition Number of Coal Plants + References No definition available. + Details
Name: | ajg_NumberOfCoalPlants
Namespace Prefix: | ajg_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Number of Variable Interest Entities + References No definition available. + Details
Name: | ajg_NumberOfVariableInterestEntities
Namespace Prefix: | ajg_
Data Type: | xbrli:decimalItemType
Balance Type: | na
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_ScheduleOfEquityMethodInvestmentsLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Details
Name: | invest_InvestmentAxis=ajg_FourteenTwoThousandNineEraCleanCoalProductionPlantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis=ajg_CleanCoalInvestmentsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=ajg_ControllingInterestMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=ajg_OneTwoThousandElevenEraCleanCoalProductionPlantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_StatementEquityComponentsAxis=us-gaap_NoncontrollingInterestMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | invest_InvestmentAxis=ajg_NineteenTwoThousandElevenEraCleanCoalProductionPlantsMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |