Acquisitions and Discontinued Operations - Components of Income (Loss) from Discontinued Operations, Net of Taxes for Education Lending Business (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	$ 2,293	$ 2,325	$ 2,264
Net interest income (expense) after provision for loan and lease losses	2,234	2,195	2,035
Noninterest expense	2,759	2,820	2,818
Income taxes	326	271	231
Income (loss) from discontinued operations, net of taxes	(39)	40	23
Segment, Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	89	105	119
Provision (credit) for loan and lease losses	21	20	9
Net interest income (expense) after provision for loan and lease losses	68	85	110
Noninterest income	(101)	76	62
Noninterest expense	29	95	135
Income (loss) before income taxes	(62)	66	37
Income taxes	(23)	26	14
Income (loss) from discontinued operations, net of taxes	(39)	40	23
Education Lending [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Income (loss) before income taxes	(79)	(79)	25
Income taxes	(30)	(29)	9
Income (loss) from discontinued operations, net of taxes	(49)	(50)	16
Education Lending [Member] | Segment, Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net interest income	77	105	119
Provision (credit) for loan and lease losses	21	20	9
Net interest income (expense) after provision for loan and lease losses	56	85	110
Noninterest income	(111)	(136)	(49)
Noninterest expense	$ 24	$ 28	$ 36