Trading Assets and Liabilities (Details) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	$ 25,559	$ 16,150
Trading liabilities	3,277	4,879
U.S. Treasury [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	4,733	3,391
US Government agency issued or guaranteed [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	114	122
US Government-sponsored Enterprises Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	27	210
Asset-backed Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	240	236
Corporate and foreign bonds [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	7,687	6,180
Other securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	0	12
Precious metals [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	9,212	2,274
Trading liabilities	0	524
Securities sold, not yet purchased [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	982	1,722
Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	3,546	3,725
Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	$ 2,295	$ 2,633