Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	$ (25)	$ 1	$ (11)	$ 7
Hedge gain (loss) to be reclassified during next twelve months			(10)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(2)	(4)	(6)	6
Compensation and benefits
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	(4)	1	(4)	9
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	0	1	13
Other general expenses
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	(1)	1	3	2
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(1)	(1)	(2)	(2)
Interest expense
Derivative [Line Items]
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	(1)	(1)	(1)
Other income (expense)
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	(20)	(1)	(10)	(4)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	$ (1)	$ (2)	$ (4)	$ (4)