Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Derivative [Line Items]
Gain (Loss) Currently Recognized in Accumulated Other Comprehensive Loss	$ (3)	$ 11	$ (14)	$ 18
Hedge gain (loss) to be reclassified during next twelve months			(12)
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	(3)	(3)	(9)	3
Compensation and benefits
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	(4)	0	(8)	9
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	1	1	14
Other general expenses
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	0	3	3	5
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	(1)	(2)	(3)
Interest expense
Derivative [Line Items]
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	0	0	(1)	(1)
Other income (expense)
Derivative [Line Items]
Hedge gain (loss) to be reclassified during next twelve months	1	8	(9)	4
Gain (Loss) reclassified from Accumulated Other Comprehensive Loss into Income (Effective Portion)	$ (3)	$ (3)	$ (7)	$ (7)