Restructuring - Narrative (Details) - 2017 Plan $ in Millions	3 Months Ended	12 Months Ended	24 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2018 USD ($) job_elimination	Dec. 31, 2018 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Additional expected cost	$ 200	$ 200	$ 200
Additional expected cash payments	150
Additional expected con-cash charges	50
Expected cost	1,225	1,225	$ 1,225
Number of positions eliminated | job_elimination			4,366
Incurred restructuring cost		485	$ 982
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Expected cost	450	450	450
Incurred restructuring cost		115	414
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Expected cost	130	130	130
Incurred restructuring cost		47	80
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Expected cost	65	65	65
Incurred restructuring cost		28	36
Asset impairments
Restructuring Cost and Reserve [Line Items]
Expected cost	50	50	50
Incurred restructuring cost		13	39
Other Restructuring
Restructuring Cost and Reserve [Line Items]
Expected cost	$ 530	530	530
Incurred restructuring cost		$ 282	$ 413
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