Acquisitions and Discontinued Operations - Combined Assets and Liabilities of Discontinued Operations (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014	Dec. 31, 2013
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	$ 506	$ 653	$ 409	$ 617
Held-to-maturity securities	5,005	5,015	4,826
Portfolio 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]
Cash and due from banks	15	19	19
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	2,246	2,324	4,427
Trust securities at fair value			1,796
Total liabilities		3	1,819
Discontinued Operations [Member] | Seller Note [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio loans at fair value			28
Discontinued Operations [Member] | Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio 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
Accrued expense and other liabilities		3	3
Discontinued Operations [Member] | Portfolio [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio loans at fair value	$ 187	$ 191	$ 143