Trading Assets and Liabilities (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	$ 26,556	$ 16,150
Trading liabilities	3,948	4,879
U.S. Treasury [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	4,037	3,391
US Government agency issued or guaranteed [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	111	122
US Government-sponsored enterprises [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	22	210
Asset-backed securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	220	236
Corporate and foreign bonds [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	8,325	6,180
Equity securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	752	12
Precious metals [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	9,945	2,274
Trading liabilities	0	524
Securities sold, not yet purchased [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	1,605	1,722
Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading assets	3,144	3,725
Derivatives [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	$ 2,343	$ 2,633