Summary of Significant Commitments (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Long-term Purchase Commitment
Commitments	$ 4,019
Commitments to Extend Credit
Long-term Purchase Commitment
Commitments	59,411	53,403
Financial Standby Letter of Credit
Long-term Purchase Commitment
Commitments	4,019	4,281
Forward Contracts
Long-term Purchase Commitment
Commitments	4,068	5,322
Noncancelable Lease Obligations
Long-term Purchase Commitment
Commitments	742	769
Private Equity Funds
Long-term Purchase Commitment
Commitments	96	121
Purchase Commitment
Long-term Purchase Commitment
Commitments	89	87
Capital Additions
Long-term Purchase Commitment
Commitments	38	29
Capital Lease Obligations
Long-term Purchase Commitment
Commitments	$ 19	$ 24