Related Party Transactions - Summary of Related Party Transactions (Detail) (USD $) In Millions, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2011
Assets:
Cash and due from banks	$ 1,385	$ 1,616
Interest bearing deposits with banks	15,313	25,454
Federal funds sold and securities purchased under resale agreements	11,678	3,109
Trading assets	38,322	38,800
Loans	61,452	51,867	49,600
Other	7,528	6,369
Total assets	203,132	210,280	188,442
Liabilities:
Deposits	121,335	139,729	132,841
Trading liabilities	20,875	14,186
Short-term borrowings	14,113	16,009
Long-term debt	20,963	16,709
Other	8,277	4,223
Total liabilities	185,563	191,778
Parent and Other Subsidiaries of Common Parent [Member]
Assets:
Cash and due from banks	458	263
Interest bearing deposits with banks	908	1,416
Federal funds sold and securities purchased under resale agreements		228
Trading assets	22,697	22,367
Loans	2,843	858
Other	977	248
Total assets	27,883	25,380
Liabilities:
Deposits	16,805	18,153
Trading liabilities	24,695	25,298
Short-term borrowings	2,725	2,916
Long-term debt	3,989	3,988
Other	631	451
Total liabilities	$ 48,845	$ 50,806