Marketable Securities - Narrative (Details)	9 Months Ended
Sep. 30, 2017 item
Percentage of asset-backed securities rated AAA/A-1+, Aaa/P-1, or AAA/F1+	79.90%
Number of rating agencies for asset backed securities that must be either Moody's or Standard and Poor's	1
Minimum
Number of rating agencies for which asset backed securities must be rated	2

Percentage of asset-backed securities in the available for sale portfolio that were rated AAA or A-1+ by Standard and Poor's and/or Aaa or P-1 by Moody's and/or AAA or F1+ by Fitch.

No definition available.

Name:	mmm_AvailableForSaleAssetBackedSecuritiesPercentageOfSecuritiesRatedAtHighestGradeDisclosure
Namespace Prefix:	mmm_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant