LHFI by Credit Quality Indicator (Additional Information) (Detail) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014	Dec. 31, 2014
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired Financing Receivable, Interest Income, Cash Basis Method	$ 1,000,000		$ 1,000,000
Loans Receivable, Fair Value Disclosure	268,000,000			272,000,000
Loans and Leases Receivable, Gross	132,380,000,000	[1]		133,112,000,000	[1]
Residential Guaranteed [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	655,000,000			632,000,000
Federally Guaranteed Student Loans [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans and Leases Receivable, Gross	4,337,000,000			4,827,000,000
Federal Home Loan Bank Advances [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans Pledged as Collateral	$ 31,000,000,000			$ 31,200,000,000
Residential Portfolio Segment [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Government Guarantee Percent	2.00%			2.00%

[1] Includes loans of consolidated VIEs of $277 million and $288 million at March 31, 2015 and December 31, 2014, respectively.