Asset Quality - Nonperforming Assets and Past Due Loans (Detail) - USD ($) $ in Millions	Sep. 30, 2015	Dec. 31, 2014	Sep. 30, 2014
Receivables [Abstract]
Total nonperforming loans	$ 400	$ 418	$ 401
Nonperforming loans held for sale	0	0	0
OREO	17	18	16
Other nonperforming assets			1
Total nonperforming assets	417	436	418
Nonperforming assets from discontinued operations-education lending	8	11	9
Restructured loans included in nonperforming loans	159	157	137
Restructured loans with an allocated specific allowance	71	82	115
Specifically allocated allowance for restructured loans	29	34	30
Accruing loans past due 90 days or more	54	96	71
Accruing loans past due 30 through 89 days	$ 271	$ 235	$ 340