Asset Quality - Nonperforming Assets and Past Due Loans (Detail) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Financing Receivable, Recorded Investment, Past Due [Line Items]
Total nonperforming loans	$ 507	$ 625
OREO	48	51
Other nonperforming assets	1	0
Total nonperforming assets	556	676
Nonperforming assets from discontinued operations-education lending	5	5
TDRs included in nonperforming loans	193	141
TDRs with an allocated specific allowance	72	59
Specifically allocated allowance for restructured loans	25	27
Accruing loans past due 90 days or more	85	87
Accruing loans past due 30 through 89 days	340	404
Purchased credit impaired loans	835	865
Restructured loans	24	22
Foreclosed Residential Real Estate [Member]
Financing Receivable, Recorded Investment, Past Due [Line Items]
Carrying value of foreclosed residential real estate	$ 29	$ 29