Restructuring - Schedule of Restructuring and Related Expenses (Details) - 2017 Plan $ in Millions	3 Months Ended	6 Months Ended	30 Months Ended
	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 127	$ 218	$ 1,200
Estimated Remaining Costs	150	150	150
Expected total cost	1,350	1,350	1,350
Expected non-cash expense	100	100	100
Workforce reduction
Restructuring Cost and Reserve [Line Items]
Costs incurred	78	102	516
Estimated Remaining Costs	14	14	14
Expected total cost	530	530	530
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Costs incurred	4	15	95
Estimated Remaining Costs	35	35	35
Expected total cost	130	130	130
Contract termination costs incurred	2	3	9
Expected contract termination cost remaining	15	15	15
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Costs incurred	5	14	50
Estimated Remaining Costs	30	30	30
Expected total cost	80	80	80
Contract termination costs incurred	4	13	46
Expected contract termination cost remaining	80	80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Costs incurred	2	2	41
Estimated Remaining Costs	4	4	4
Expected total cost	45	45	45
Other costs associated with restructuring and separation
Restructuring Cost and Reserve [Line Items]
Costs incurred	38	85	498
Estimated Remaining Costs	67	67	67
Expected total cost	565	565	565
Contract termination costs incurred	1	3	91
Expected contract termination cost remaining	$ 95	$ 95	$ 95