Derivatives and Hedging - Schedule of amounts of derivative gains (losses) recognized in the Consolidated Financial Statements (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Gain (loss) recognized in accumulated other comprehensive income	$ 18	$ (25)	$ (9)
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	(9)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(1)	(10)	(17)
Compensation and Benefits
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	12	8	4
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	14	2	4
Other General Expenses
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	4	(13)	(3)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(5)	(4)	(1)
Interest Expense
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	0	0	0
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	(1)	(1)	(9)
Other Income (Expense)
Derivative [Line Items]
Estimated pretax losses currently included within Accumulated Other Comprehensive Loss that will be reclassified to earnings in next twelve months	2	(20)	(10)
Gain (loss) reclassified from accumulated other comprehensive loss into income (effective portion)	$ (9)	$ (7)	$ (11)