Variable Interest Entities - Additional Information (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Maximum Exposure to Loss	$ 9,666	$ 9,105
Trading assets arising due to "failed sale" accounting treatment	31	140
Long-term liabilities arising due to "failed sale" accounting treatment	34	147
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	$ 3,438	$ 2,212