Fair Value Measurement - Changes in Level 3, Supplemental Caption Data (Details 2a) (USD $) In Millions, unless otherwise specified			3 Months Ended		6 Months Ended
	Jun. 30, 2013	Dec. 31, 2012	Jun. 30, 2013 Available-for-sale Securities	Jun. 30, 2012 Available-for-sale Securities	Jun. 30, 2013 Available-for-sale Securities	Jun. 30, 2012 Available-for-sale Securities
Fair Value, Option, Quantitative Disclosures
Level Three Liabilities As Percentage Of Total Firm Liabilities At Fair Value	16.00%	18.00%
Realized gains and losses recorded in income on AFS securities			$ 3	$ (260)	$ (15)	$ (164)
Unrealized gains and losses recorded in OCI on AFS securities			$ (3)	$ (55)	$ 11	$ (140)