Restructuring (Details) $ in Millions	Mar. 31, 2018 USD ($)
Separation and Other Headcount-related Costs [Member]
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	$ 558
Asset-related Charges [Member]
Restructuring Cost and Reserve [Line Items]
Total costs incurred to date	243
Minimum [Member]
Restructuring Cost and Reserve [Line Items]
Expected pre-tax accounting charges	825
Separation and other headcount-related costs	560
Accelerated depreciation and asset impairment and other related charges	265
Maximum [Member]
Restructuring Cost and Reserve [Line Items]
Expected pre-tax accounting charges	900
Separation and other headcount-related costs	600
Accelerated depreciation and asset impairment and other related charges	$ 300