XML 76 R63.htm IDEA: XBRL DOCUMENT
v3.20.2

Stock Option Plans - Stock Options Outstanding and Exercisable (Detail) - $ / shares shares in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2020 | Dec. 31, 2019
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | $ 43.71 |
Range of Exercise Prices, maximum | $ 86.17 |
Option Outstanding, Number Outstanding | 8.0 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 3 years 11 months 1 day |
Option Outstanding, Weighted Average Exercise Price | $ 63.82 | $ 56.40
Options Exercisable, Number Exercisable | 2.5 |
Option Exercisable, Weighted Average Exercise Price | $ 47.03 |
Exercise Prices Range $ 43.71 - $ 43.71 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 43.71 |
Range of Exercise Prices, maximum | $ 43.71 |
Option Outstanding, Number Outstanding | 1.5 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 2 years 5 months 15 days |
Option Outstanding, Weighted Average Exercise Price | $ 43.71 |
Options Exercisable, Number Exercisable | 0.8 |
Option Exercisable, Weighted Average Exercise Price | $ 43.71 |
Exercise Prices Range $ 46.17 - $ 46.87 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 46.17 |
Range of Exercise Prices, maximum | $ 46.87 |
Option Outstanding, Number Outstanding | 1.3 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 1 year 1 month 6 days |
Option Outstanding, Weighted Average Exercise Price | $ 46.41 |
Options Exercisable, Number Exercisable | 1.3 |
Option Exercisable, Weighted Average Exercise Price | $ 46.41 |
Exercise Prices Range $ 49.55 - $ 56.86 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 49.55 |
Range of Exercise Prices, maximum | $ 56.86 |
Option Outstanding, Number Outstanding | 1.3 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 3 years 5 months 15 days |
Option Outstanding, Weighted Average Exercise Price | $ 56.83 |
Options Exercisable, Number Exercisable | 0.4 |
Option Exercisable, Weighted Average Exercise Price | $ 56.81 |
Exercise Prices Range $ 70.74 - $ 70.74 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 70.74 |
Range of Exercise Prices, maximum | $ 70.74 |
Option Outstanding, Number Outstanding | 1.1 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 4 years 5 months 15 days |
Option Outstanding, Weighted Average Exercise Price | $ 70.74 |
Option Exercisable, Weighted Average Exercise Price | 70.74 |
Exercise Prices Range $ 79.59 - $ 79.59 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 79.59 |
Range of Exercise Prices, maximum | $ 79.59 |
Option Outstanding, Number Outstanding | 1.2 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 5 years 5 months 12 days |
Option Outstanding, Weighted Average Exercise Price | $ 79.59 |
Exercise Prices Range $ 86.17 - $ 86.17 [Member] |  |
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items] |  |
Range of Exercise Prices, minimum | 86.17 |
Range of Exercise Prices, maximum | $ 86.17 |
Option Outstanding, Number Outstanding | 1.6 |
Option Outstanding, Weighted Average Remaining Contractual Term (in years) | 6 years 5 months 12 days |
Option Outstanding, Weighted Average Exercise Price | $ 86.17 |

X
- Definition Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingWeightedAverageExercisePrice
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
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_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition The floor of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeLowerRangeLimit
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of shares reserved for issuance pertaining to the outstanding exercisable stock options as of the balance sheet date in the customized range of exercise prices for which the market and performance vesting condition has been satisfied. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfExercisableOptions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of shares reserved for issuance pertaining to the outstanding stock options as of the balance sheet date for all option plans in the customized range of exercise prices. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(i)-(ii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeNumberOfOutstandingOptions
Namespace Prefix: | us-gaap_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | instant

X
- Definition The ceiling of a customized range of exercise prices for purposes of disclosing shares potentially issuable under outstanding stock option awards on all stock option plans and other required information pertaining to awards in the customized range. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeUpperRangeLimit
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (e)(1) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsOutstandingWeightedAverageRemainingContractualTerm2
Namespace Prefix: | us-gaap_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Weighted average exercise price as of the balance sheet date for those equity-based payment arrangements exercisable and outstanding. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(1)(iii) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
Name: | us-gaap_SharebasedCompensationSharesAuthorizedUnderStockOptionPlansExercisePriceRangeExercisableOptionsWeightedAverageExercisePrice1
Namespace Prefix: | us-gaap_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range01Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range02Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range03Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range04Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range05Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_ShareBasedCompensationSharesAuthorizedUnderStockOptionPlansByExercisePriceRangeAxis=ajg_Range06Member
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |