LHFI by Credit Quality Indicator (Detail) - USD ($) $ in Millions		Mar. 31, 2018		Dec. 31, 2017
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[1]	$ 142,618		$ 143,181
Financing Receivable, Recorded Investment, Nonaccrual Status	[3]	712	[2]	674	[4]
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	66,321		66,356
Financing Receivable, Recorded Investment, Nonaccrual Status		216	[2]	215	[4]
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		5,352		5,317
Financing Receivable, Recorded Investment, Nonaccrual Status		46	[2]	24	[4]
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,651		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]	27,165	[8]	27,136	[9]
Financing Receivable, Recorded Investment, Nonaccrual Status		253	[2],[8]	206	[4],[9]
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	10,241		10,626
Financing Receivable, Recorded Investment, Nonaccrual Status		169	[2]	203	[4]
Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	256		298
Financing Receivable, Recorded Investment, Nonaccrual Status		16	[2]	11	[4]
Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		8,941		8,729
Financing Receivable, Recorded Investment, Nonaccrual Status		8	[2]	7	[4]
Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		11,869		12,140
Financing Receivable, Recorded Investment, Nonaccrual Status		4	[2]	7	[4]
Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,518		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		64,453		64,546
Pass | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		5,152		5,126
Pass | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,597		3,770
Criticized Accruing | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,652		1,595
Criticized Accruing | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		154		167
Criticized Accruing | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		54		33
FICO Score 700 and Above [Member] | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	23,732		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]	8,621		8,946
FICO Score 700 and Above [Member] | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	204		240
FICO Score 700 and Above [Member] | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		8,145		7,929
FICO Score 700 and Above [Member] | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		8,867		9,094
FICO Score 700 and Above [Member] | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,034		1,088
FICO Score Between 620 and 699 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	2,655		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]	1,174		1,242
FICO Score Between 620 and 699 | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	45		50
FICO Score Between 620 and 699 | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		755		757
FICO Score Between 620 and 699 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		2,270		2,344
FICO Score Between 620 and 699 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		385		395
FICO Score Below 620 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	778		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]	446		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]	41		43
FICO Score Below 620 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	732		702
FICO Score Below 620 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	$ 99		$ 99

[1] Includes loans of consolidated VIEs of $171 million and $179 million at March 31, 2018 and December 31, 2017, respectively.

[2] Nonaccruing loans past due 90 days or more totaled $417 million. Nonaccruing loans 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] Nonaccruing loans past due 90 days or more totaled $357 million. Nonaccruing loans 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 $3.6 billion and $3.7 billion of lease financing, and $788 million and $778 million of installment loans at March 31, 2018 and December 31, 2017, respectively.

[6] Excludes $6.7 billion and $6.6 billion of guaranteed student loans and $611 million and $560 million of guaranteed residential mortgages at March 31, 2018 and December 31, 2017, respectively, for which there was nominal risk of principal loss due to the government guarantee.

[7] Includes $188 million and $196 million of LHFI measured at fair value at March 31, 2018 and December 31, 2017, respectively.

[8] Includes $188 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.