Commercial Paper and Other Short-Term Borrowings (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2014	Dec. 31, 2013
Commercial Paper and Short-Term Borrowings
Federal funds purchased and securities sold under repurchase agreements with weighted average interest rates of 0.11% and 0.07% at June 30, 2014 and December 31, 2013	$ 137	$ 39
Commercial paper, with weighted average interest rates of 0.16% and 0.19% at June 30, 2014 and December 31, 2013, respectively	2,733	2,524
Total commercial paper and other short-term borrowings	$ 2,870	$ 2,563
Federal funds purchased and securities sold under repurchase agreements
Commercial Paper and Short-Term Borrowings
Weighted average interest rate (as a percent)	0.11%	0.07%
Commercial paper
Commercial Paper and Short-Term Borrowings
Weighted average interest rate (as a percent)	0.16%	0.19%