LHFI by Credit Quality Indicator (Detail) - USD ($) $ in Millions		Sep. 30, 2018		Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[1]	$ 147,215		$ 143,181
Financing Receivable, Recorded Investment, Nonaccrual Status	[3]	695	[2]	674	[4]
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	68,203		66,356
Financing Receivable, Recorded Investment, Nonaccrual Status		256	[2]	215	[4]
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		6,618		5,317
Financing Receivable, Recorded Investment, Nonaccrual Status		43	[2]	24	[4]
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,137		3,804
Financing Receivable, Recorded Investment, Nonaccrual Status		0	[2]	1	[4]
Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[7]	28,187	[8]	27,136	[9]
Financing Receivable, Recorded Investment, Nonaccrual Status		225	[2],[8]	206	[4],[9]
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	9,669		10,626
Financing Receivable, Recorded Investment, Nonaccrual Status		149	[2]	203	[4]
Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	197		298
Financing Receivable, Recorded Investment, Nonaccrual Status		9	[2]	11	[4]
Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		10,100		8,729
Financing Receivable, Recorded Investment, Nonaccrual Status		7	[2]	7	[4]
Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		12,010		12,140
Financing Receivable, Recorded Investment, Nonaccrual Status		6	[2]	7	[4]
Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,603		1,582
Financing Receivable, Recorded Investment, Nonaccrual Status		0	[2]	0	[4]
Pass | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		66,224		64,546
Pass | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		6,418		5,126
Pass | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,038		3,770
Criticized Accruing | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,723		1,595
Criticized Accruing | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		157		167
Criticized Accruing | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		99		33
FICO Score 700 and Above [Member] | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	24,968		23,602
FICO Score 700 and Above [Member] | Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	8,208		8,946
FICO Score 700 and Above [Member] | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	163		240
FICO Score 700 and Above [Member] | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		9,197		7,929
FICO Score 700 and Above [Member] | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		8,967		9,094
FICO Score 700 and Above [Member] | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,084		1,088
FICO Score Between 620 and 699 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	2,499		2,721
FICO Score Between 620 and 699 | Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	1,046		1,242
FICO Score Between 620 and 699 | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	27		50
FICO Score Between 620 and 699 | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		866		757
FICO Score Between 620 and 699 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		2,321		2,344
FICO Score Between 620 and 699 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		401		395
FICO Score Below 620 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	720		813
FICO Score Below 620 | Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	415		438
FICO Score Below 620 | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	7		8
FICO Score Below 620 | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	37		43
FICO Score Below 620 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	722		702
FICO Score Below 620 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	$ 118		$ 99

[1] Includes loans of consolidated VIEs of $159 million and $179 million at September 30, 2018 and December 31, 2017, respectively.

[2] Includes nonaccruing LHFI past due 90 days or more of $348 million. Nonaccruing LHFI past due fewer than 90 days include nonaccrual loans modified in TDRs, performing second lien loans where the first lien loan is nonperforming, and certain energy-related commercial loans.

[3] Nonaccruing restructured loans are included in total nonaccrual loans/NPLs.

[4] Includes nonaccruing LHFI past due 90 days or more of $357 million. Nonaccruing LHFI past due fewer than 90 days include nonaccrual loans modified in TDRs, performing second lien loans where the first lien loan is nonperforming, and certain energy-related commercial loans.

[5] Includes $3.8 billion and $3.7 billion of lease financing, and $838 million and $778 million of installment loans at September 30, 2018 and December 31, 2017, respectively.

[6] Excludes $7.0 billion and $6.6 billion of guaranteed student loans and $452 million and $560 million of guaranteed residential mortgages at September 30, 2018 and December 31, 2017, respectively, for which there was nominal risk of principal loss due to the government guarantee.

[7] Includes $168 million and $196 million of LHFI measured at fair value at September 30, 2018 and December 31, 2017, respectively.

[8] Includes $168 million of loans measured at fair value, the majority of which were accruing current.

[9] Includes $196 million of loans measured at fair value, the majority of which were accruing current.

[10] For substantially all loans with refreshed FICO scores below 620, the borrower’s FICO score at the time of origination exceeded 620 but has since deteriorated as the loan has seasoned.