Acquisitions and Discontinued Operations - Components of Assets and Liabilities of Education Lending Business (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	$ 187	$ 191	$ 143
Loans, net of unearned income	57,953	57,381	55,445
Total assets	2,246	2,324	4,427
Trust accrued expense and other liabilities at fair value	1,308	1,621	1,297
Total liabilities		3	1,819
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans, net of unearned income	2,032	2,104	2,318
Less: Allowance for loan and lease losses	25	29	34
Net loans	2,194	2,266	4,320
Accrued income and other assets	36	38	41
Total assets	2,246	2,324	4,427
Trust securities at fair value			1,796
Total liabilities		3	1,819
Trust [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value			1,893
Trust accrued income and other assets at fair value			19
Trust accrued expense and other liabilities at fair value			20
Portfolio [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value	187	191	143
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	1
Loans, net of unearned income	2,032	2,104	2,318
Less: Allowance for loan and lease losses	25	29	34
Net loans	2,194	2,266	4,320
Accrued income and other assets	36	38	41
Total assets	2,231	2,305	4,380
Total liabilities			1,816
Education Lending [Member] | Trust [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans at fair value			1,893
Trust accrued income and other assets at fair value			19
Trust accrued expense and other liabilities at fair value			20
Trust securities at fair value			1,796
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	$ 187	$ 191	$ 143