Acquisitions and Discontinued Operations - Components of Assets of Education Lending Business (Detail) - USD ($)	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value		$ 191,000,000	$ 201,000,000
Loans, net of unearned income	$ 60,085,000,000	57,381,000,000	56,155,000,000
Loans held for sale at fair value	0	0	0
Total assets	2,086,000,000	2,324,000,000	2,421,000,000
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans, net of unearned income	1,891,000,000	2,104,000,000	2,174,000,000
Less: Allowance for loan and lease losses	23,000,000	29,000,000	31,000,000
Net loans	1,868,000,000	2,266,000,000	2,344,000,000
Accrued income and other assets	33,000,000	38,000,000	40,000,000
Total assets	2,086,000,000	2,324,000,000	2,421,000,000
Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans held for sale at fair value	169,000,000
Portfolio [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value		191,000,000	201,000,000
Loans held for sale at fair value	169,000,000
Education Lending [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Held-to-maturity securities	1,000,000	1,000,000	1,000,000
Loans, net of unearned income	1,891,000,000	2,104,000,000	2,174,000,000
Less: Allowance for loan and lease losses	23,000,000	29,000,000	31,000,000
Net loans	1,868,000,000	2,266,000,000	2,344,000,000
Accrued income and other assets	33,000,000	38,000,000	40,000,000
Total assets	2,071,000,000	2,305,000,000	2,385,000,000
Education Lending [Member] | Portfolio [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value		$ 191,000,000	$ 201,000,000
Loans held for sale at fair value	$ 169,000,000