LHFI Considered Impaired (Additional Information) (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017		Dec. 31, 2016	Mar. 31, 2016
Financing Receivable, Impaired [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 130	[1]		$ 108	[2]
Impaired Financing Receivable, Interest Income, Cash Basis Method	1			2
Accrual Loans [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 2,500		$ 2,500
Percentage Of Accruing Troubled Debt Restructurings, Current	98.00%		97.00%
Consumer Other Direct [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment	$ 1			$ 1	[2]
Consumer Other Direct [Member] | Loans modified prior to 2016 [Member]
Financing Receivable, Impaired [Line Items]
Financing Receivable, Modifications, Post-Modification Recorded Investment			$ 41

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

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