Trading Securities (Detail) - USD ($) $ in Millions		Mar. 31, 2018	Dec. 31, 2017
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	[1]	$ 5,112	$ 5,093
Trading liabilities		1,737	1,283
US Treasury Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		182	157
Trading liabilities		698	577
US Government Agencies Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		238	395
US States and Political Subdivisions Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		123	61
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		699	700
Trading liabilities		1	0
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		804	655
Trading liabilities		453	289
Commercial Paper [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		169	118
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities		51	56
Trading liabilities		5	9
Derivative Financial Instruments, Assets [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	[2]	657	802
Loans [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading Securities	[3]	2,189	2,149
Derivative Financial Instruments, Liabilities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Trading liabilities	[2]	$ 580	$ 408

[1] Includes trading securities pledged as collateral where counterparties have the right to sell or repledge the collateral of $1,248 million and $1,086 million at March 31, 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.