Reconciliation of the Beginning and Ending Balances for Fair Valued Assets and Liabilities Measured on a Recurring Basis Using Significant Unobservable Inputs (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018		Mar. 31, 2017		Dec. 31, 2017	Dec. 31, 2016
Derivative contracts, net [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		$ 1		$ 17		$ 0	$ 6
Included in earnings		(6)	[1]	48	[2]
OCI		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		1		(1)
Transfers to other balance sheet line items		6		(36)
Transfers into Level 3		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy		0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		16	[1],[3]	30	[2],[4]
US States and Political Subdivisions Debt Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value				4			4
Included in earnings				0
OCI				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases				0
Sales				0
Settlements				0
Transfers to other balance sheet line items				0
Transfers into Level 3				0
Transferred Out of Level 3 in The Fair Value Hierarchy				0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income				0
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0		71		59	74
Included in earnings		0		0
OCI		0		1	[5]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		2		2
Transfers to other balance sheet line items		0		0
Transfers into Level 3		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy		(57)		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		0		0
Asset-backed Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0		9		8	10
Included in earnings		0		0
OCI		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		1		1
Transfers to other balance sheet line items		0		0
Transfers into Level 3		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy		(7)		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		0		0
Corporate Debt Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0		5		5	5
Included in earnings		0		0
OCI		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		0		0
Transfers to other balance sheet line items		0		0
Transfers into Level 3		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy		(5)		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		0		0
Available-for-sale Securities [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		0		89		72	93
Included in earnings		0		0
OCI		0		1	[5]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		3		3
Transfers to other balance sheet line items		0		0
Transfers into Level 3		0		0
Transferred Out of Level 3 in The Fair Value Hierarchy		(69)		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		0		0
Residential Mortgage, Loans Held For Sale [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value				6			12
Included in earnings				0
OCI				0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases				0
Sales				(14)
Settlements				0
Transfers to other balance sheet line items				(2)
Transfers into Level 3				10
Transferred Out of Level 3 in The Fair Value Hierarchy				0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income	[4]			0
Loans Held-For-Investment [Member]
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset Value		188		221		$ 196	$ 222
Included in earnings		(2)	[6]	0
OCI		0		0
Fair Value, Measurement with Unobservable Inputs Reconciliation, Recurring Basis, Asset, Purchases		0		0
Sales		0		0
Settlements		7		6
Transfers to other balance sheet line items		0		(1)
Transfers into Level 3		1		4
Transferred Out of Level 3 in The Fair Value Hierarchy		0		0
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss) Included in Other Income		$ (3)	[3],[6]	$ 0	[4]

[1] Includes issuances, fair value changes, and expirations. Amount related to residential IRLCs is recognized in Mortgage production related income, amount related to commercial IRLCs is recognized in Commercial real estate related income, and amount related to Visa derivative liability is recognized in Other noninterest expense.

[2] Includes issuances, fair value changes, and expirations. Amount related to residential IRLCs is recognized in Mortgage production related income and amount related to Visa derivative liability is recognized in Other noninterest expense.

[3] Change in unrealized gains/(losses) included in earnings during the period related to financial assets still held at March 31, 2018.

[4] Change in unrealized gains included in earnings during the period related to financial assets still held at March 31, 2017.

[5] Amounts recognized in OCI are included in change in net unrealized losses on securities AFS, net of tax.

[6] Amounts are generally included in Mortgage production related income; however, the mark on certain fair value loans is included in Other noninterest income.