Acquisition, Divestiture, and Discontinued Operations - Additional Information (Detail)						3 Months Ended	9 Months Ended	12 Months Ended
	Aug. 01, 2016 USD ($)	Dec. 08, 2015 USD ($)	Oct. 30, 2015 $ / shares shares	Oct. 29, 2015 USD ($)	Sep. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Sep. 30, 2014 USD ($)	Dec. 31, 2016 USD ($) SecurityLoan Trust TDR	Dec. 31, 2015 USD ($) SecurityLoan TDR	Dec. 31, 2014 USD ($) SecurityLoan TDR	Sep. 09, 2016 USD ($) Branch	Jun. 30, 2015 USD ($) Trust	Jan. 01, 2010 Trust
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of branches sold | Branch											18
Discontinued assets								$ 1,585,000,000	$ 1,846,000,000
Number of TDRs | SecurityLoan								4,515	4,622	4,776
Allowance for loan held as investment								$ 858,000,000	$ 796,000,000
Loans held for sale adjusted to fair value								0	0
Number of outstanding securitizations trusts | Trust												3
Proceeds from loans sold								8,572,000,000	7,333,000,000	$ 5,386,000,000
Gain on sale of loans								139,000,000	103,000,000	$ 97,000,000
Portfolio loans at fair value								$ 3,000,000	4,000,000
Loans sold, fair value									$ 162,000,000
First Niagara Financial Group, Inc. [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Total consideration to be paid	$ 4,000,000,000
Acquiree shares equivalent of acquirer common stock | shares			0.680
Cash payable per acquiree common stock | $ / shares			$ 2.30
Number of branches sold | Branch											18
Net loans											$ 439,000,000
Disposal group, deposits											$ 1,600,000,000
Pacific Crest Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of outstanding securitization trusts | Trust								3
Proceeds from sale of residual interests					$ 57,000,000
After tax loss recognized							$ 25,000,000
Number of continuing securitization trusts | Trust								8
Estimated fair value of the assets and deposits acquired					1,000,000		1,000,000
Education Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Number of TDRs | TDR								2,163	1,901	1,612
Investment recorded								$ 22,000,000	$ 21,000,000	$ 17,000,000
Allowance for loan held as investment									2,000,000	$ 1,000,000
Government Guaranteed Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from loans sold				$ 117,000,000
Private Loans [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from loans sold		$ 45,000,000
Gain on sale of loans		$ 1,000,000
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Net loans								1,541,000,000	1,800,000,000
Number of outstanding securitization trusts | Trust													10
Discontinued assets								1,585,000,000	1,846,000,000
Allowance for loan held as investment								2,000,000
Portfolio loans at fair value								$ 3,000,000	$ 4,000,000
Trust [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Loans held for sale adjusted to fair value												$ 179,000,000
Trust [Member] | Pacific Crest Securities [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Discontinued assets					1,700,000,000		1,700,000,000
Discontinued liabilities					$ 1,600,000,000		$ 1,600,000,000
Victory Capital Management [Member] | Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Cash portion in gain						$ 6,000,000