Subsequent events Cost estimates by major type of expense (Details) - Subsequent Event - 2018 Footprint Realignment Plan $ in Millions	May 01, 2018 USD ($)
Minimum
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	$ 102
Minimum | Employee termination benefits
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	60
Minimum | Other Restructuring costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	2
Minimum | Special Termination Benefit And Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	62
Minimum | Accelerated Depreciation And Other Costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	40
Maximum
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	133
Maximum | Employee termination benefits
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	70
Maximum | Other Restructuring costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	4
Maximum | Special Termination Benefit And Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	74
Maximum | Accelerated Depreciation And Other Costs
Restructuring Cost and Reserve [Line Items]
Expected restructuring charges	$ 59