Restructuring - Schedule of Restructuring and Related Expenses (Details) - 2017 Plan $ in Millions	3 Months Ended		9 Months Ended	33 Months Ended
	Sep. 30, 2019 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 USD ($)	Sep. 30, 2019 USD ($) job_elimination
Restructuring Cost and Reserve [Line Items]
Costs incurred	$ 63		$ 281
Expensed		$ 125	260	$ 1,263
Restructuring and Related Cost, Number of Positions Eliminated | job_elimination				5,353
Estimated Remaining Costs	87		87	$ 87
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	9		111	525
Estimated Remaining Costs	25		25	25
Expected total cost	550		550	550
Technology rationalization
Restructuring Cost and Reserve [Line Items]
Costs incurred	14		29	109
Estimated Remaining Costs	16		16	16
Expected total cost	125		125	125
Contract termination costs incurred	9		12	18
Expected contract termination cost remaining	20		20	20
Lease consolidation
Restructuring Cost and Reserve [Line Items]
Costs incurred	3		17	53
Estimated Remaining Costs	27		27	27
Expected total cost	80		80	80
Contract termination costs incurred	2		15	48
Expected contract termination cost remaining	80		80	80
Asset impairments
Restructuring Cost and Reserve [Line Items]
Costs incurred	5		7	46
Estimated Remaining Costs	4		4	4
Expected total cost	50		50	50
Other costs associated with restructuring and separation
Restructuring Cost and Reserve [Line Items]
Costs incurred	32		117	530
Estimated Remaining Costs	15		15	15
Expected total cost	545		545	545
Contract termination costs incurred	18		21	109
Expected contract termination cost remaining	$ 116		$ 116	$ 116