Acquisition, Divestiture, and Discontinued Operations - Components of Assets of Education Lending Business (Detail) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio loans at fair value	$ 3	$ 4
Loans net of deferred income	86,038	59,876	$ 57,381
Total assets	1,585	1,846
Unearned income on loans	826	646
Discontinued Operations [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Portfolio loans at fair value	3	4
Loans net of deferred income	1,562	1,824
Less: Allowance for loan and lease losses	24	28
Net loans	1,541	1,800
Accrued income and other assets	28	30
Total assets	1,585	1,846
Unearned income on loans	1	1
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
Portfolio loans at fair value	3	4
Loans net of deferred income	1,562	1,824
Less: Allowance for loan and lease losses	24	28
Net loans	1,541	1,800
Accrued income and other assets	28	30
Total assets	1,570	1,831
Unearned income on loans	$ 1	$ 1