XML 18 R8.htm IDEA: XBRL DOCUMENT
v3.8.0.1

Consolidated Statements Of Equity (Parenthetical) - $ / shares | 12 Months Ended
--- | ---
Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Statement of Stockholders' Equity [Abstract] |  |  |
Dividend equivalents per share (in dollars per share) | $ 1.43 | $ 1.30 | $ 1.18
Dividends declared per share (in dollars per share) | $ 1.43 | $ 1.30 | $ 1.18

X
- Definition Common Stock, Dividends Per Share, Cash, Declared + References No definition available. + Details
Name: | mmc_CommonStockDividendsPerShareCashDeclared
Namespace Prefix: | mmc_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- Definition Dividend Equivalents Per Share, Cash, Declared + References No definition available. + Details
Name: | mmc_DividendEquivalentsPerShareCashDeclared
Namespace Prefix: | mmc_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | duration

X
- References No definition available. + Details
Name: | us-gaap_StatementOfStockholdersEquityAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration