Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	9 Months Ended	33 Months Ended
	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) job_elimination	Sep. 30, 2019 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 125	$ 260	$ 1,263
Expected total cost		1,350	$ 1,350
Number of positions eliminated to date | job_elimination			5,353
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost		550	$ 550
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost		125	125
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost		80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost		50	50
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost		$ 545	$ 545
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,400
Maximum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,600