Pension and Postretirement Benefit Plans (Narratives) (Details) $ in Millions	1 Months Ended	6 Months Ended
	Mar. 31, 2015 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2014	Mar. 31, 2014 Insurer	Mar. 31, 2011 LimitedPartner
Benefit Plan Information
Estimated pension and postretirement employer contributions in current fiscal year		$ 200
Curtailment/Settlement gain	$ 17
3M Japan company provided contribution match to their defined contribution plan	6.12%
Number of additional limited partners of WG Trading Company, in addition to 3M, who objected and appealed the court's order to the United States Court of Appeals for the Second Circuit | LimitedPartner					6
Number of insurers 3M and certain benefit plans filed lawsuits on seeking insurance coverage for the WG Trading Company claim | Insurer				5
Percentage of WG Trading Company holdings in relation to total fair value of the company's total plan assets, high end of range (as a percent)			0.50%
Qualified and Non-qualified Pension Benefits
Benefit Plan Information
Company contributions year to date		183
Postretirement Benefits
Benefit Plan Information
Company contributions year to date		$ 2