Trading Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[1]	$ 5,676	$ 5,093
Trading liabilities		1,863	1,283
US Treasury Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		247	157
Trading liabilities		742	577
US Government Agencies Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		507	395
US States and Political Subdivisions Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		91	61
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		743	700
Corporate Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		820	655
Trading liabilities		411	289
Commercial Paper [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		408	118
Equity Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		67	56
Trading liabilities		12	9
Derivative Financial Instruments, Assets [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	622	802
Loans [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[3]	2,171	2,149
Derivative Financial Instruments, Liabilities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	[2]	$ 698	$ 408

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,362 million and $1,086 million at September 30, 2018 and December 31, 2017, respectively.

[2] Amounts include the impact of offsetting cash collateral received from and paid to the same derivative counterparties, and the impact of netting derivative assets and derivative liabilities when a legally enforceable master netting agreement or similar agreement exists.

[3] Includes loans related to TRS.