Significant Accounting Policies - Earnings Per Share (Details) - USD ($) $ / shares in Units, shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Earnings per share
Options outstanding not included in computation of diluted earnings per share (in shares)									18.1	8.9	2.9
Numerator:
Net income attributable to 3M	$ 1,389	$ 1,413	$ 1,290	$ 1,292	$ 969	$ 1,583	$ 1,127	$ 891	$ 5,384	$ 4,570	$ 5,349
Denominator:
Denominator for weighted average 3M common shares outstanding - basic (in shares)									577.6	577.0	588.5
Dilution associated with the Company's stock-based compensation plans (in shares)									4.6	8.1	13.5
Denominator for weighted average 3M common shares outstanding - diluted (in shares)									582.2	585.1	602.0
Earnings per share attributable to 3M common shareholders - basic (in dollars per share)	$ 2.40	$ 2.45	$ 2.24	$ 2.24	$ 1.68	$ 2.75	$ 1.95	$ 1.54	$ 9.32	$ 7.92	$ 9.09
Earnings per share attributable to 3M common shareholders - diluted (in dollars per share)	$ 2.38	$ 2.43	$ 2.22	$ 2.22	$ 1.66	$ 2.72	$ 1.92	$ 1.51	$ 9.25	$ 7.81	$ 8.89