Short-Term Borrowings (Schedule of Short-term Debt) (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Short-term Debt [Line Items]
Demand Notes	$ 3,197	$ 3,094
Short-term Bank Loans and Notes Payable	0	167
Federal Home Loan Bank, Advances, Short-term	500	3,800
Other Short-term Borrowings	500	400
Short-term borrowings	4,197	7,461
Unsecured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	3,197	3,094
Short-term Bank Loans and Notes Payable	0	167
Federal Home Loan Bank, Advances, Short-term	0	0
Other Short-term Borrowings	0	0
Short-term borrowings	3,197	3,261
Secured Debt [Member]
Short-term Debt [Line Items]
Demand Notes	0	0
Short-term Bank Loans and Notes Payable	0	0
Federal Home Loan Bank, Advances, Short-term	500	3,800
Other Short-term Borrowings	500	400
Short-term borrowings	$ 1,000	$ 4,200