Variable Interest Entities - Additional Information (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Maximum Exposure to Loss	$ 4,381	$ 4,429
Trading assets arising due to "failed sale" accounting treatment	64	140
Long-term liabilities arising due to "failed sale" accounting treatment	69	147
Asset-backed commercial paper conduits [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Expected asset increase	200
Expected decrease in liabilities	325
Maximum Exposure to Loss		2,212
Reorganization Of Variable Interest Entities, Expect Increase (Decrease) In Net Assets	125
Maximum [Member] | Asset-backed commercial paper conduits [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Maximum Exposure to Loss	$ 2,454