XML 101 R78.htm IDEA: XBRL DOCUMENT
v3.20.4

Shareholders' Equity - Components of Accumulated other comprehensive loss, net of related tax (Details) - USD ($) $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | $ 3,449 | $ 4,219 | $ 4,648
Other comprehensive income (loss) before reclassifications | 4 | (282) | (576)
Tax benefit (expense) | 62 | 58 | 43
Other comprehensive income (loss) before reclassifications, net | 66 | (224) | (533)
Amounts reclassified from accumulated other comprehensive income (loss) | 140 | 123 | 157
Tax benefit (expense) | (34) | (23) | (36)
Amounts reclassified from accumulated other comprehensive income (loss), net | 106 | 100 | 121
Total other comprehensive income (loss) attributable to Aon shareholders | 172 | (124) | (412)
Ending Balance | 3,583 | 3,449 | 4,219
Cumulative Effect, Period of Adoption, Adjustment |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (6) |  | 492
Ending Balance |  | (6) |
Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | 3,443 |  | 5,140
Ending Balance |  | 3,443 |
Change in Fair Value of Investments |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (12) | (15) | (25)
Other comprehensive income (loss) before reclassifications | 1 | (10) | (15)
Tax benefit (expense) | 0 | 1 | 18
Other comprehensive income (loss) before reclassifications, net | 1 | (9) | 3
Amounts reclassified from accumulated other comprehensive income (loss) | 15 | 14 | 11
Tax benefit (expense) | (3) | (2) | (3)
Amounts reclassified from accumulated other comprehensive income (loss), net | 12 | 12 | 8
Total other comprehensive income (loss) attributable to Aon shareholders | 13 | 3 | 11
Ending Balance | 1 | (12) | (15)
Change in Fair Value of Investments | Cumulative Effect, Period of Adoption, Adjustment |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (1)
Change in Fair Value of Investments | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (26)
Foreign Currency Translation Adjustments |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (1,305) | (1,319) | (879)
Other comprehensive income (loss) before reclassifications | 258 | 15 | (437)
Tax benefit (expense) | 2 | (1) | (3)
Other comprehensive income (loss) before reclassifications, net | 260 | 14 | (440)
Amounts reclassified from accumulated other comprehensive income (loss) | 0 | 0 | 0
Tax benefit (expense) | 0 | 0 | 0
Amounts reclassified from accumulated other comprehensive income (loss), net | 0 | 0 | 0
Total other comprehensive income (loss) attributable to Aon shareholders | 260 | 14 | (440)
Ending Balance | (1,045) | (1,305) | (1,319)
Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjustment |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 0
Foreign Currency Translation Adjustments | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (879)
Post-retirement Benefit Obligations |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (2,716) | (2,575) | (2,592)
Other comprehensive income (loss) before reclassifications | (255) | (287) | (124)
Tax benefit (expense) | 60 | 58 | 28
Other comprehensive income (loss) before reclassifications, net | (195) | (229) | (96)
Amounts reclassified from accumulated other comprehensive income (loss) | 125 | 109 | 146
Tax benefit (expense) | (31) | (21) | (33)
Amounts reclassified from accumulated other comprehensive income (loss), net | 94 | 88 | 113
Total other comprehensive income (loss) attributable to Aon shareholders | (101) | (141) | 17
Ending Balance | (2,817) | (2,716) | (2,575)
Post-retirement Benefit Obligations | Cumulative Effect, Period of Adoption, Adjustment |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | 0
Post-retirement Benefit Obligations | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (2,592)
AOCI attributable to parent |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | (4,033) | (3,909) | (3,496)
Ending Balance | (3,861) | (4,033) | (3,909)
AOCI attributable to parent | Cumulative Effect, Period of Adoption, Adjustment |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance |  |  | (1)
AOCI attributable to parent | Cumulative Effect, Period of Adoption, Adjusted Balance |  |  |
Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] |  |  |
Beginning Balance | $ (4,033) |  | $ (3,497)
Ending Balance |  | $ (4,033) |

X
- Definition Changes in Accumulated Other Comprehensive Income (Loss) [Roll Forward] + References No definition available. + Details
Name: | aon_ChangesInAccumulatedOtherComprehensiveIncomeLossRollForward
Namespace Prefix: | aon_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount before tax and reclassification adjustments of other comprehensive income (loss) attributable to parent. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
Name: | us-gaap_OciBeforeReclassificationsBeforeTaxAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount after tax, before reclassification adjustments, of other comprehensive income (loss), attributable to parent. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=121640130&loc=d3e1436-108581 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
Name: | us-gaap_OciBeforeReclassificationsNetOfTaxAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of tax expense (benefit) allocated to other comprehensive income (loss) before reclassification adjustment from accumulated other comprehensive income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e640-108580 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossBeforeReclassificationsTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount after tax of other comprehensive income (loss) attributable to parent entity. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1B -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669625-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 50 -Paragraph 1A -Subparagraph (c)(3) -URI http://asc.fasb.org/extlink&oid=109239629&loc=SL4573702-111684 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569643-111683 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 1A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669619-108580 Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 19 -URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4569616-111683 + Details
Name: | us-gaap_OtherComprehensiveIncomeLossNetOfTaxPortionAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount before tax of reclassification adjustments of other comprehensive income (loss) attributable to parent. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 + Details
Name: | us-gaap_ReclassificationFromAociCurrentPeriodBeforeTaxAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount after tax of reclassification adjustments of other comprehensive income (loss) attributable to parent. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 14A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL7669686-108580 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 55 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=121640130&loc=d3e1436-108581 + Details
Name: | us-gaap_ReclassificationFromAociCurrentPeriodNetOfTaxAttributableToParent
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount of tax expense (benefit) of reclassification adjustment from accumulated other comprehensive income (loss). + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=121641772&loc=d3e640-108580 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 17A -URI http://asc.fasb.org/extlink&oid=121641772&loc=SL34724391-108580 + Details
Name: | us-gaap_ReclassificationFromAociCurrentPeriodTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of stockholders' equity (deficit), net of receivables from officers, directors, owners, and affiliates of the entity, attributable to both the parent and noncontrolling interests. Amount excludes temporary equity. Alternate caption for the concept is permanent equity. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 45 -Paragraph 24 -URI http://asc.fasb.org/extlink&oid=115929471&loc=d3e21930-107793 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 17 -URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32136-110900 Reference 3: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=120397183&loc=d3e187085-122770 Reference 4: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 45 -Paragraph 23 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=115929471&loc=d3e21914-107793 Reference 5: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 7 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22644-107794 Reference 6: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 326 -SubTopic 10 -Section 65 -Paragraph 4 -Subparagraph (d) -URI http://asc.fasb.org/extlink&oid=121646688&loc=SL121648383-210437 Reference 7: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 16 -URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4568740-111683 Reference 9: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (f)(2) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 55 -Paragraph 4I -URI http://asc.fasb.org/extlink&oid=120409616&loc=SL4590271-111686 Reference 11: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 40 -Section 65 -Paragraph 2 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=121370832&loc=SL117420844-207641 Reference 12: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 825 -SubTopic 10 -Section 50 -Paragraph 28 -Subparagraph (f) -URI http://asc.fasb.org/extlink&oid=75031198&loc=d3e14064-108612 Reference 13: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 45 -Paragraph 20 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=118261656&loc=d3e32211-110900 Reference 14: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 45 -Paragraph 5 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=115929471&loc=d3e21711-107793 Reference 15: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 15 -URI http://asc.fasb.org/extlink&oid=108774443&loc=SL4568447-111683 Reference 16: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (f)(1) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 17: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571 Reference 18: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 250 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (b)(3) -URI http://asc.fasb.org/extlink&oid=109234566&loc=d3e22499-107794 Reference 19: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 235 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.4-08(g)(1)(ii)) -URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690 Reference 20: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 830 -SubTopic 30 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6450520&loc=d3e32583-110901 Reference 21: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 65 -Paragraph 15 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=121322162&loc=SL121327923-165333 Reference 22: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 65 -Paragraph 8 -Subparagraph (d)(2) Reference 23: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 65 -Paragraph 8 -Subparagraph (d)(3) + Details
Name: | us-gaap_StockholdersEquityIncludingPortionAttributableToNoncontrollingInterest
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Details
Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_CumulativeEffectPeriodOfAdoptionAxis=srt_CumulativeEffectPeriodOfAdoptionAdjustedBalanceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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

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

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

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