Commercial Paper and Other Short-Term Borrowings (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2012	Dec. 31, 2011
Schedule of commercial paper and short term debt
Federal funds purchased and securities sold under repurchase agreements with weighted average interest rates of 0.22% and 0.06% at June 30, 2012 and December 31, 2011, respectively	$ 198	$ 597
Commercial paper, with weighted average interest rates of 0.28% and 0.22% at June 30, 2012 and December 31, 2011, respectively	2,837	2,498
Other borrowed funds:
Term federal funds purchased, with weighted average interest rates of 0.15% at December 31, 2011		50
Federal Home Loan Bank advances with weighted average interest rates of 0.48% at December 31, 2011		500
All other borrowed funds, with weighted average interest rates of 0.73% at December 31, 2011		38
Total commercial paper and other short-term borrowings	$ 3,035	$ 3,683