Short-Term Borrowings (Schedule of Short-term Debt) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Short-term Debt [Line Items]
Demand Notes	$ 3,404	$ 3,225
Federal Home Loan Bank, Advances, Short-term	750	3,570
Securities Sold under Agreements to Repurchase, Gross	759	1,500
Other Short-term Borrowings	250	250
Short-term borrowings	5,163	8,545
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,404	3,225
Federal Home Loan Bank, Advances, Short-term	0	0
Securities Sold under Agreements to Repurchase, Gross	0	0
Other Short-term Borrowings	0	0
Short-term borrowings	3,404	3,225
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Federal Home Loan Bank, Advances, Short-term	750	3,570
Securities Sold under Agreements to Repurchase, Gross	759	1,500
Other Short-term Borrowings	250	250
Short-term borrowings	$ 1,759	$ 5,320