Property, Plant and Equipment (Depreciation Expense, Software Amortization and Capitalized Interest) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Depreciation expense	$ 1,005	$ 1,002	$ 958
Interest capitalized during development and construction	139	118	$ 84
Property plant and equipment, net of accumulated depreciation mortgaged, pledged or subject to liens	$ 10,000	$ 10,000