Significant Accounting Policies - Consolidated Statement of Comprehensive Income as Adjusted (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income including noncontrolling interest	$ 1,437	$ 1,434	$ 4,589	$ 4,047
Other comprehensive income (loss), net of tax:
Defined benefit pension and postretirement plans adjustment	119	116	359	271
Total other comprehensive income (loss), net of tax	(135)	316	100	144
Comprehensive income (loss) including noncontrolling interest	1,302	1,750	4,689	4,191
Comprehensive income (loss) attributable to 3M	$ 1,300	1,745	$ 4,683	4,190
Under Prior Method
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net income including noncontrolling interest		1,417		3,998
Other comprehensive income (loss), net of tax:
Defined benefit pension and postretirement plans adjustment		127		304
Total other comprehensive income (loss), net of tax		327		177
Comprehensive income (loss) including noncontrolling interest		1,744		4,175
Comprehensive income (loss) attributable to 3M		$ 1,739		$ 4,174