Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended		27 Months Ended
	Mar. 31, 2019 USD ($) job_elimination	Dec. 31, 2018 USD ($)	Mar. 31, 2019 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Additional expected cost		$ 200
Additional expected cash investment		150
Additional expected non-cash expense		$ 50
Expected total cost	$ 1,225		$ 1,225
Number of positions eliminated to date | job_elimination			4,491
Costs incurred	91		$ 1,073
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost	450		450
Costs incurred	24		438
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost	130		130
Costs incurred	11		91
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost	65		65
Costs incurred	9		45
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost	50		50
Costs incurred	0		39
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost	530		530
Costs incurred	$ 47		$ 460
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination	4,800
Maximum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination	5,400