Indebtedness (Narrative) (Details) (USD $)	Sep. 30, 2013	Dec. 31, 2012
Line of Credit Facility [Line Items]
Short-term borrowings, carrying value	$ 3,668,000,000	$ 2,419,000,000
Line of Credit Facility, Maximum Borrowing Capacity	8,000,000,000
364-day revolving credit, expiring February 11, 2014 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,000,000,000