Trading Securities (Detail) - USD ($) $ in Millions		Sep. 30, 2019	Dec. 31, 2018
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[1]	$ 7,104	$ 5,506
Trading liabilities		1,380	1,604
US Treasury Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		212	262
Trading liabilities		538	801
US Government Agencies Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		319	188
US States and Political Subdivisions Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		43	54
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities		0	3
Corporate Debt Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		628	700
Trading liabilities		539	385
Commercial Paper [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		122	190
Equity Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		86	73
Trading liabilities		20	5
Derivative Financial Instruments, Assets [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[2]	1,770	639
Loans [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI	[3]	2,862	2,540
Derivative Financial Instruments, Liabilities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Trading liabilities	[2]	274	410
Trading Loans [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		2,862	2,540
Trading liabilities		9	0
Fair Value, Recurring [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		7,104	5,506
Fair Value, Recurring [Member] | 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			860
Fair Value, Recurring [Member] | Asset-backed Securities [Member]
Debt and Equity Securities, FV-NI [Line Items]
Debt Securities, Trading, and Equity Securities, FV-NI		7	0
Fair Value, Recurring [Member] | Commercial Mortgage Backed Securities [Member] | 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		51	0
Fair Value, Recurring [Member] | Residential Mortgage Backed Securities [Member] | 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		$ 1,004	$ 860

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,284 million and $1,442 million at September 30, 2019 and December 31, 2018, 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.