Quarterly Financial Data (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale/revaluation of assets after tax	$ (133)			$ 9	$ (7)	$ 20
Gain (loss) on sale of assets, after tax, per share	$ (0.24)			$ 0.02	$ (0.02)	$ 0.04
Impairment and restructuring, after tax				$ 10			$ 16	$ 12
Impairment and restructuring per share, after tax				$ 0.02			$ 0.03	$ 0.02
Acquisition-related expenses, after-tax	$ 2			$ 9	$ 9
Acquisition-related expenses, per share	$ 0.00			$ 0.02	$ 0.01
Impairment, settlement, and restructuring, after tax	$ 93	$ 41	$ 105		$ 196
Impairment, settlement, and restructuring per share, after tax	$ 0.16	$ 0.08	$ 0.18		$ 0.35
Tax expense (credit) related to the tax reform and certain out of period discretes	$ (46)	$ 5	$ 19	$ (17)	$ 29	$ (3)	$ (7)	$ 14
Tax expense (credit) related to the tax reform and certain out of period discretes per share	$ (0.08)	$ 0.01	$ 0.03	$ (0.03)	$ 0.05	$ (0.01)	$ (0.01)	$ 0.03