Asset Quality - Post-Modification Outstanding Recorded Investment by Concession Type for Our Commercial Accruing and Nonaccruing TDRs (Parenthetical) (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Receivables [Abstract]
Additional funds to borrowers related to lending related commitments	$ 5	$ 5	$ 2