Restructuring Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	15 Months Ended
	Mar. 31, 2018 USD ($) job_elimination	Mar. 31, 2018 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Expected total cost	$ 1,025	$ 1,025
Number of positions eliminated to date | job_elimination		3,123
Costs incurred	74	$ 571
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost	450	450
Costs incurred	33	332
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost	130	130
Costs incurred	10	43
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost	85	85
Costs incurred	3	11
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost	50	50
Costs incurred	1	27
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost	310	310
Costs incurred	$ 27	$ 158
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination	4,200
Maximum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination	4,800