Significant Accounting Policies - Consolidated Statement of Comprehensive Income as Adjusted (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Net income including noncontrolling interest	$ 1,627	$ 1,310
Other comprehensive income (loss), net of tax:
Defined benefit pension and postretirement plans adjustment	119	108
Total other comprehensive income (loss), net of tax	(45)	(289)
Comprehensive income (loss) including noncontrolling interest	1,582	1,021
Comprehensive income (loss) attributable to 3M	$ 1,578	1,022
Under Prior Method
Net income including noncontrolling interest		1,294
Other comprehensive income (loss), net of tax:
Defined benefit pension and postretirement plans adjustment		119
Total other comprehensive income (loss), net of tax		(278)
Comprehensive income (loss) including noncontrolling interest		1,016
Comprehensive income (loss) attributable to 3M		$ 1,017