Derivative Instruments and Hedging Activities - Net Gains (Losses) Related to Derivatives Designated as Cash Flow Hedges and Net Investment Hedges (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in AOCI	$ (238)	$ 277	$ 367
Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Net derivative gains recognized in earnings	103	85	75
Cash flow hedges
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in AOCI	(95)	(3)	284
Gains (losses) reclassified from AOCI into earnings	108	195	174
Net derivative gains recognized in earnings	110	191	176
Cash flow hedges | Interest rate contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in AOCI	(113)	(6)	301
Cash flow hedges | Interest rate contracts | Interest Income (Expense)
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reclassified from AOCI into earnings	91	192	190
Cash flow hedges | Interest rate contracts | Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recognized in earnings due to ineffectiveness	2	(4)	2
Cash flow hedges | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in AOCI	18	3	(17)
Cash flow hedges | Foreign exchange contracts | Other Non-Interest Income
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) reclassified from AOCI into earnings	17	3	(16)
Net investment hedges | Foreign exchange contracts
Derivative Instruments, Gain (Loss) [Line Items]
Gains (losses) recorded in AOCI	$ (143)	$ 280	$ 83