XML 82 R63.htm IDEA: XBRL DOCUMENT
v3.19.2

Derivatives - Narrative (Details) € in Billions, £ in Billions |  | 1 Months Ended | 3 Months Ended | 6 Months Ended | 12 Months Ended |
--- | --- | --- | --- | --- | --- | ---
Sep. 20, 2018 GBP (£) | Mar. 31, 2019 USD ($) | Jan. 31, 2019 USD ($) | Jun. 30, 2019 USD ($) | Mar. 31, 2019 USD ($) | Jun. 30, 2019 USD ($) | Jun. 30, 2018 USD ($) | Dec. 31, 2018 USD ($) | Mar. 31, 2019 EUR (€)
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Total consideration |  |  |  |  |  | $ 5,925,000,000 | $ 192,000,000 |  |
Increase in cumulative translation adjustments due to gain on net investment hedge |  |  |  | $ 9,000,000 |  | 9,000,000 |  |  |
Foreign Exchange Forward |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Unrealized loss |  |  |  | 11,000,000 |  |  |  |  |
Unrealized gain |  |  |  |  |  | 31,000,000 |  |  |
Treasury Lock |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Payments for derivative settlement |  |  | $ 122,000,000 |  | $ 6,000,000 |  |  |  |
Jardine Lloyd Thompson Group plc |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Total consideration | £ 5.2 |  |  |  |  | $ 5,568,000,000 |  |  |
Jardine Lloyd Thompson Group plc | Foreign Exchange Forward |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Derivative, loss on derivative |  |  |  | $ 26,000,000 |  |  |  |  |
Jardine Lloyd Thompson Group plc | Treasury Lock |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Unrealized loss |  |  |  |  |  |  |  | $ 116,000,000 |
Derivative hedges, assets |  |  |  |  |  |  |  | $ 2,000,000,000 |
Senior Notes |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Proceeds from issuance of debt |  |  | $ 5,000,000,000 |  |  |  |  |  |
Senior Notes | Jardine Lloyd Thompson Group plc |  |  |  |  |  |  |  |  |
Derivative [Line Items] |  |  |  |  |  |  |  |  |
Payments for derivative settlement |  | $ 7,300,000 |  |  |  |  |  |  |
Proceeds from issuance of debt | € |  |  |  |  |  |  |  |  | € 1.1
Net investment hedge, threshold percentage of the equity balance |  |  |  |  |  | 80.00% |  |  |
Decrease in net investment hedges |  |  |  |  |  | $ 9,000,000 |  |  |

X
- Definition Net Investment Hedge, Threshold Percentage of the Equity Balance + References No definition available. + Details
Name: | mmc_NetInvestmentHedgeThresholdPercentageoftheEquityBalance
Namespace Prefix: | mmc_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Payments for Derivative Settlement + References No definition available. + Details
Name: | mmc_PaymentsforDerivativeSettlement
Namespace Prefix: | mmc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Gain (loss) on hedging derivative instrument or the foreign currency transaction gain (loss) on the nonderivative hedging instrument designated as a hedge of a net investment in foreign operations related to hedge ineffectiveness, which is included in earnings in the period. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4C -Subparagraph (d)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624171-113959 + Details
Name: | us-gaap_AmountOfIneffectivenessOnNetInvestmentHedges
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of consideration transferred, consisting of acquisition-date fair value of assets transferred by the acquirer, liabilities incurred by the acquirer, and equity interest issued by the acquirer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6613-128477 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 50 -Paragraph 1 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479 Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 805 -SubTopic 30 -Section 30 -Paragraph 7 -URI http://asc.fasb.org/extlink&oid=109124213&loc=d3e6578-128477 + Details
Name: | us-gaap_BusinessCombinationConsiderationTransferred1
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Face (par) amount of debt instrument at time of issuance. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399 Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 835 -SubTopic 30 -Section 55 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400 + Details
Name: | us-gaap_DebtInstrumentFaceAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Amount of increase (decrease) in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
Name: | us-gaap_DerivativeGainLossOnDerivativeNet
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Amount of increase in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
Name: | us-gaap_DerivativeGainOnDerivative
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Carrying amount as of the balance sheet date of the asset arising from derivative instruments and hedging activities, which are expected to be converted into cash or otherwise disposed of within a year or the normal operating cycle, if longer. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.8) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
Name: | us-gaap_DerivativeInstrumentsAndHedges
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_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of decrease in the fair value of derivatives recognized in the income statement. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4A -Subparagraph (b)(1) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5618551-113959 + Details
Name: | us-gaap_DerivativeLossOnDerivative
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Amount, after tax, of reclassification from accumulated other comprehensive income (AOCI) of gain (loss) from increase (decrease) in fair value of net investment hedge. + References Reference 1: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 815 -SubTopic 10 -Section 50 -Paragraph 4CCC -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109980867&loc=SL109998896-113959 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Publisher FASB -Name Accounting Standards Codification -Topic 220 -SubTopic 10 -Section 45 -Paragraph 10A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=114867106&loc=SL7669646-108580 + Details
Name: | us-gaap_TranslationAdjustmentForNetInvestmentHedgeIncreaseDecreaseNetOfTax
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_TreasuryLockMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_BusinessAcquisitionAxis=mmc_JardineLloydThompsonGroupplcMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |