Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - Cash Flow Hedging - Foreign exchange contracts - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	$ 11	$ (1)	$ 18	$ (19)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(3)	(2)	3	(6)
Compensation and benefits
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	0	10	9	8
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	1	1	14	2
Other General Expenses
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	3	(4)	5	(9)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(1)	(1)	(3)	(2)
Interest Expense
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	0	0	0	0
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	0	(1)	(1)
Other Income (Expense)
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	8	(7)	4	(18)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	$ (3)	$ (2)	$ (7)	$ (5)