Quarterly Financial Data (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017
Restructuring Cost and Reserve [Line Items]
Impairment and restructuring, after tax			$ 16	$ 12		$ 69		$ 8
Impairment and restructuring per share, after tax			$ 0.03	$ 0.02		$ 0.12		$ 0.01
Impairment, settlement, and restructuring, after tax	$ 196				$ 46		$ 21
Impairment, settlement, and restructuring per share, after tax	$ 0.35				$ 0.08		$ 0.04
Acquisition-related expenses	$ 9
Acquisition-related expenses, per share	$ 0.01
Tax expense (credit) related to the tax reform and certain out of period discretes	$ 29	$ 3	$ 7	$ (14)	$ 370
Tax expense (credit) related to the tax reform and certain out of period discretes per share	$ 0.05	$ 0.01	$ 0.01	$ (0.03)	$ 0.65
Gain (loss) on sale/revaluation of assets after tax	$ 7	$ (20)				$ (10)	$ 22
Gain (loss) on sale of assets, after tax, per share	$ 0.02	$ (0.04)				$ (0.02)	$ 0.04
Out of period tax discrete expense (income) items								$ 4
Out of period tax discrete expense (income) items, per share								$ 0.01
Extinguishment of Debt, Gain (Loss), Net of Tax						$ 7
Extinguishment of Debt, Gain (Loss), Per Share, Net of Tax						$ 0.01
Extinguishment of Debt, Amount						$ 559			$ 559