LHFI by Credit Quality Indicator (Detail) - USD ($) $ in Millions		Dec. 31, 2017		Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[1]	$ 143,181		$ 143,298
Financing Receivable, Recorded Investment, Nonaccrual Status	[3]	674	[2]	845	[4]
Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[5]	66,356		69,213
Financing Receivable, Recorded Investment, Nonaccrual Status		215	[2]	390	[4]
Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		5,317		4,996
Financing Receivable, Recorded Investment, Nonaccrual Status		24	[2]	7	[4]
Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,804		4,015
Financing Receivable, Recorded Investment, Nonaccrual Status		1	[2]	17	[4]
Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[7]	27,136	[8]	26,137	[9]
Financing Receivable, Recorded Investment, Nonaccrual Status		206	[2],[8]	177	[4],[9]
Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	10,626		11,912
Financing Receivable, Recorded Investment, Nonaccrual Status		203	[2]	235	[4]
Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	298		404
Financing Receivable, Recorded Investment, Nonaccrual Status		11	[2]	12	[4]
Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		8,729		7,771
Financing Receivable, Recorded Investment, Nonaccrual Status		7	[2]	6	[4]
Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		12,140		10,736
Financing Receivable, Recorded Investment, Nonaccrual Status		7	[2]	1	[4]
Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,582		1,410
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		64,546		66,961
Pass | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		5,126		4,574
Pass | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		3,770		3,914
Criticized Accruing | Commercial and Industrial [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,595		1,862
Criticized Accruing | Commercial Real Estate [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		167		415
Criticized Accruing | Commercial Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		33		84
FICO Score 700 and Above [Member] | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	23,602		22,194
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]	8,946		9,826
FICO Score 700 and Above [Member] | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	240		292
FICO Score 700 and Above [Member] | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		7,929		7,008
FICO Score 700 and Above [Member] | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		9,094		7,642
FICO Score 700 and Above [Member] | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		1,088		974
FICO Score Between 620 and 699 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	2,721		3,042
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]	1,242		1,540
FICO Score Between 620 and 699 | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6]	50		96
FICO Score Between 620 and 699 | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		757		703
FICO Score Between 620 and 699 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		2,344		2,381
FICO Score Between 620 and 699 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment		395		351
FICO Score Below 620 | Residential Nonguaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	813		901
FICO Score Below 620 | Home Equity Line of Credit [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	438		546
FICO Score Below 620 | Residential Construction [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[6],[10]	8		16
FICO Score Below 620 | Consumer Other Direct [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	43		60
FICO Score Below 620 | Consumer Indirect [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	702		713
FICO Score Below 620 | Credit Card Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans held for investment	[10]	$ 99		$ 85

[1] Includes loans of consolidated VIEs of $179 million and $211 million at December 31, 2017 and December 31, 2016, respectively.

[2] 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.

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

[4] Nonaccruing loans past due 90 days or more totaled $360 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 $3.7 billion of lease financing at both December 31, 2017 and 2016, and $778 million and $729 million of installment loans at December 31, 2017 and 2016, respectively.

[6] Excludes $6.6 billion and $6.2 billion of guaranteed student loans and $560 million and $537 million of guaranteed residential mortgages at December 31, 2017 and 2016, respectively, for which there was nominal risk of principal loss due to the government guarantee.

[7] Includes $196 million and $222 million of LHFI measured at fair value at December 31, 2017 and 2016, respectively.

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

[9] Includes $222 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.