LHFI Considered Impaired (Additional Information) (Detail) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2018		Sep. 30, 2017		Sep. 30, 2018		Sep. 30, 2017		Dec. 31, 2017
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Gross	[1]	$ 147,215				$ 147,215				$ 143,181
Transfer of Loans Held-for-sale to Portfolio Loans		5		$ 6		23		$ 16
Financing Receivable, Modifications, Post-Modification Recorded Investment		55	[2]	102	[3]	230	[4]	362	[5]
Other Real Estate	[6]	52				52				57
Accrual Loans [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Modifications, Recorded Investment		$ 2,300				$ 2,300				$ 2,400
Percentage Of Accruing Troubled Debt Restructurings, Current		97.00%				97.00%				96.00%
Proceeds due from FHA or VA [Member]
Financing Receivable, Impaired [Line Items]
Other Real Estate		$ 49				$ 49				$ 45
Consumer Other Direct [Member]
Financing Receivable, Impaired [Line Items]
Loans and Leases Receivable, Gross		10,100				10,100				$ 8,729
Financing Receivable, Modifications, Post-Modification Recorded Investment		$ 2	[2]	$ 2	[3]	$ 6	[4]	$ 6	[5]

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

[2] Includes loans modified under the terms of a TDR that were charged-off during the period.

[3] Includes loans modified under the terms of a TDR that were charged-off during the period.

[4] Includes loans modified under the terms of a TDR that were charged-off during the period.

[5] Includes loans modified under the terms of a TDR that were charged-off during the period.

[6] Does not include foreclosed real estate related to loans insured by the FHA or guaranteed by the VA. Proceeds due from the FHA and the VA are recorded as a receivable in Other assets in the Consolidated Balance Sheets until the property is conveyed and the funds are received. The receivable related to proceeds due from the FHA and the VA totaled $49 million and $45 million at September 30, 2018 and December 31, 2017, respectively.