Variable Interest Entities - Summary of Assets and Liabilities Related to Consolidated Variable Interest Entities (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Interest bearing deposits with banks	$ 15,313	$ 25,454
Other assets	7,528	6,369
Long term debt	20,963	16,709
Variable interest entities [Member]
Interest bearing deposits with banks	83	108
Other assets	566	520
Low Income Housing Limited Asset Partnership, Total	649	628
Long term debt	55	55
Other liabilities	181	166
Low Income Housing Limited Liability Partnership, Total	$ 236	$ 221