Quarterly Financial Data (Narrative) (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019
Restructuring Cost and Reserve [Line Items]
Gain (loss) on sale/revaluation of assets after tax	$ 8	$ 54	$ 18		$ (133)			$ 9
Gain (loss) on sale of assets, after tax, per share	$ 0.01	$ 0.10	$ 0.03		$ (0.24)			$ 0.02
Impairment and restructuring per share, after tax	$ 0.03	$ 0.01	$ 0.02	$ 0.06	$ 0.16	$ 0.08	$ 0.18	$ 0.02
Acquisition-related expenses, after-tax	$ 3				$ 2			$ 9
Acquisition-related expenses, per share	$ 0.01				$ 0.00			$ 0.02
Impairment, settlement, and restructuring, after tax	$ 20	$ 5	$ 12	$ 32	$ 93	$ 41	$ 105	$ 10
Tax expense (credit) related to the tax reform and certain out of period discretes	$ 19	$ (8)	$ (1)	$ (7)	$ (46)	$ 5	$ 19	$ (17)
Tax expense (credit) related to the tax reform and certain out of period discretes per share	$ 0.04	$ (0.02)	$ (0.00)	$ (0.01)	$ (0.08)	$ 0.01	$ 0.03	$ (0.03)
Gain (loss) on debt extinguishment, after tax	$ 1	$ (300)	$ (11)
Gain (loss) on debt extinguishment, per share	$ 0.00	$ (0.53)	$ (0.02)
Gain (loss) on embedded derivative	$ 2	$ 15
Gain (loss) on embedded derivative, per share	$ 0.00	$ 0.03