LHFI by Credit Quality Indicator (Additional Information) (Detail) (USD $)	Dec. 31, 2014		Dec. 31, 2013
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	$ 133,112,000,000	[1]	$ 127,877,000,000	[1]
Residential Guaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	632,000,000		3,416,000,000
Federally Guaranteed Student Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	4,827,000,000		5,545,000,000
FICO Score 700 and Above [Member] | Residential Guaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	632,000,000		3,416,000,000
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral	$ 31,200,000,000		$ 31,200,000,000

[1] Includes noncontrolling interest of $108 million and $119 million at December 31, 2014 and December 31, 2013, respectively.