Activity in the Allowance for Credit Losses (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Dec. 31, 2012	Dec. 31, 2011
Components:
Balance at beginning of period	$ 2,219	$ 2,505
Provision for loan losses	204	313
Provision(Benefit) for unfunded commitments	(8)	(4)
Loan charge-offs	(273)	(463)
Loan recoveries	47	41
Balance at end of period	2,205	2,400
Loans and Leases Receivable, Allowance	2,152	2,348	2,174	2,457
Unfunded commitments reserve	53	52
Allowance for credit losses	$ 2,205	$ 2,400