Acquisition, Divestiture, and Discontinued Operations - Combined Assets and Liabilities of Discontinued Operations (Detail) - USD ($)	Sep. 30, 2016	Dec. 31, 2015	Sep. 30, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	$ 749,000,000	$ 607,000,000	$ 470,000,000	$ 653,000,000
Held-to-maturity securities	8,995,000,000	4,897,000,000	4,936,000,000
Portfolio loans at fair value	3,000,000	4,000,000
Loans, net of unearned income	85,528,000,000	59,876,000,000	60,085,000,000
Portfolio loans held for sale at fair value	0	0	0
Total assets	1,654,000,000	1,846,000,000	2,086,000,000
Unearned income on loans (less than)	1,069,000,000	646,000,000	645,000,000
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash and due from banks	15,000,000	15,000,000	15,000,000
Held-to-maturity securities	1,000,000	1,000,000	1,000,000
Portfolio loans at fair value	3,000,000	4,000,000	0
Loans, net of unearned income	1,625,000,000	1,824,000,000	1,891,000,000
Less: Allowance for loan and lease losses	18,000,000	28,000,000	23,000,000
Net loans	1,610,000,000	1,800,000,000	1,868,000,000
Portfolio loans held for sale at fair value	0	0	169,000,000
Accrued income and other assets	28,000,000	30,000,000	33,000,000
Total assets	1,654,000,000	1,846,000,000	2,086,000,000
Unearned income on loans (less than)	$ 1,000,000	$ 0	$ 0