Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	6 Months Ended	30 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($) job_elimination	Jun. 30, 2019 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Restructuring charges	$ 125	$ 204
Expected total cost	1,350	1,350	$ 1,350
Number of positions eliminated to date | job_elimination			5,091
Costs incurred	127	218	$ 1,200
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected total cost	530	530	530
Costs incurred	78	102	516
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected total cost	130	130	130
Costs incurred	4	15	95
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected total cost	80	80	80
Costs incurred	5	14	50
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected total cost	45	45	45
Costs incurred	2	2	41
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected total cost	565	565	565
Costs incurred	$ 38	$ 85	$ 498
Minimum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,000
Maximum
Restructuring Cost and Reserve [Line Items]
Expected number of positions eliminated | job_elimination		5,600