Fair Value Measurements - Additional Information (Detail) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2013
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale			$ 12,000,000
Fair value of OREO property re-evaluated period		90 days
Loan, net of allowance	54,611,000,000	53,609,000,000	51,681,000,000
Loans in portfolio	143,000,000	143,000,000	143,000,000
Average maturity of short-term financial instruments	Less than six months
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	401,000,000	611,000,000	434,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	401,000,000	611,000,000	434,000,000
Segment, Discontinued Operations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	4,320,000,000	4,458,000,000	5,037,000,000
Segment, Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	4,320,000,000	4,458,000,000	5,037,000,000
Segment, Discontinued Operations [Member] | Fair Value [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	1,900,000,000	2,000,000,000	2,200,000,000
Loans in portfolio	143,000,000	147,000,000	154,000,000
Loans in the trusts	1,900,000,000	2,000,000,000	2,300,000,000
Securities issued by the education lending securitization trusts	1,800,000,000	1,800,000,000	2,100,000,000
Segment, Discontinued Operations [Member] | Carrying Amount [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	2,300,000,000	2,400,000,000	2,600,000,000
Residential Real Estate Mortgage Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	2,200,000,000	2,200,000,000	2,200,000,000
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale			12,000,000
Level 3 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	401,000,000	611,000,000	434,000,000
Level 3 [Member] | Commercial Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	$ 0	$ 0	$ 12,000,000