Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Parenthetical) (Detail) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015	Jun. 30, 2015
Receivables [Abstract]
Additional funds to borrowers related to lending related commitments	$ 7	$ 9	$ 8