Indebtedness (Credit Facilities) (Details) - USD ($)	Dec. 31, 2017	Oct. 01, 2017	Jan. 27, 2017
Line of Credit Facility [Line Items]
Committed Credit Facilities	$ 8,000,000,000
Commercial Paper	0
364-day revolving credit, expiring February 6, 2018 [Member]
Line of Credit Facility [Line Items]
Committed Credit Facilities	2,000,000,000		$ 2,000,000,000
Multi-year revolving credit, expiring February 28, 2021 [Member]
Line of Credit Facility [Line Items]
Committed Credit Facilities	2,500,000,000
Multi-year revolving credit, expiring October 1, 2022 [Member]
Line of Credit Facility [Line Items]
Committed Credit Facilities	$ 3,500,000,000	$ 3,500,000,000