Fair Value Measurements - Additional Information (Detail) (USD $)	6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Unfunded commitments	$ 84,000,000
Investment liquidation minimum period	1 year
Investment liquidation maximum period	9 years
Fair value of OREO property re-evaluated period	90 days
Nonexit price methodology for valuing loan portfolio	1.37%
Loan, net of allowance	52,225,000,000	51,934,000,000	48,717,000,000
Loans in portfolio	151,000,000
Average maturity of short-term financial instruments	Less than six months
Segment, Discontinued Operations [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	4,951,000,000	5,146,000,000	5,404,000,000
Segment, Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	4,951,000,000	5,146,000,000	5,404,000,000
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	2,000,000,000
Carrying Amount [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	402,000,000	599,000,000	656,000,000
Carrying Amount [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	2,200,000,000	2,600,000,000	2,800,000,000
Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	402,000,000	599,000,000	656,000,000
Fair Value [Member] | Segment, Discontinued Operations [Member] | Education Lending [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loan, net of allowance	2,100,000,000	2,300,000,000	2,400,000,000
Loans in portfolio	151,000,000	157,000,000	73,000,000
Loans in the trusts	2,300,000,000	2,400,000,000	2,600,000,000
Securities issued by the education lending securitization trusts	2,100,000,000	2,200,000,000	2,400,000,000
Level 3 [Member] | Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	402,000,000	599,000,000	656,000,000
Principal Investments Direct [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total other investments	426,000,000
Commercial Loans [Member] | Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Commercial loan held-for-sale	$ 0	$ 9,000,000	$ 15,000,000