Restructuring - Schedule of Restructuring and Related Expenses (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)
Restructuring Cost and Reserve [Line Items]
Estimated Remaining Costs	$ 451	$ 451
2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	155	299
Expected total cost	750	750
Workforce reduction | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	102	205
Estimated Remaining Costs	98	98
Expected total cost	303	303
Technology rationalization | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	7	10
Estimated Remaining Costs	136	136
Expected total cost	146	146
Expected contract termination cost remaining	9	9
Lease consolidation | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	1	4
Estimated Remaining Costs	76	76
Expected total cost	80	80
Contract termination costs incurred	1	5
Expected contract termination cost remaining	80	80
Asset impairments | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	11	24
Estimated Remaining Costs	16	16
Expected total cost	40	40
Other Restructuring | 2017 Plan
Restructuring Cost and Reserve [Line Items]
Costs incurred	34	56
Estimated Remaining Costs	125	125
Expected total cost	$ 181	$ 181