Asset Quality - Allowance for Loan and Lease Losses and Corresponding Loan Balances (Parenthetical) (Detail) (USD $) In Billions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2012
Receivables [Abstract]
Loans carried at fair value	$ 2.3	$ 2.5	$ 2.6