Asset Quality - Nonperforming Assets and Past Due Loans (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Financing Receivable, Modifications [Line Items]
Total nonperforming loans	$ 625	$ 387
OREO	51	14
Other nonperforming assets	0	2
Total nonperforming assets	676	403
Nonperforming assets from discontinued operations-education lending	5	7
TDRs included in nonperforming loans	141	159
TDRs with an allocated specific allowance	59	69
Specifically allocated allowance for TDRs	27	30
Accruing loans past due 90 days or more	87	72
Accruing loans past due 30 through 89 days	404	208
Purchased credit impaired loans	865	11
Restructured loans	22	21
Foreclosed Residential Real Estate [Member]
Financing Receivable, Modifications [Line Items]
Carrying value of foreclosed residential real estate	$ 29	$ 11