Indebtedness (Credit Facilities) (Details) (USD $) In Billions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 8.0
364-day revolving credit, expiring February 10, 2015 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2.0
Multi-year revolving credit, expiring February 28, 2019 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	2.5
Line of Credit Facility, Initiation Date	Feb. 28, 2014
Multi-year revolving credit, expiring October 25, 2016 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 3.5