Business Segment Information Business Segment Information (Restructuring Costs) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016
Segment Reporting Information [Line Items]
Restructuring Charges	$ 26	$ 24
Restructuring Reserve	123	115	$ 97	$ 91
Employee Retention and Severances Expenses and Other Benefits-Related Costs [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	26	24
Restructuring Reserve	109	94	83	70
Economic Development Costs [Member]
Segment Reporting Information [Line Items]
Restructuring Charges	0	0
Restructuring Reserve	$ 14	$ 21	$ 14	$ 21