Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income (Loss), Net	$ 1	$ (7)	$ 0
Provision for income taxes	407	(411)	1
Net Income (Loss)	(3,112)	$ 891	$ 537	[1]
Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income (Loss)	5
Pension and Other Postretirement | Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income (Loss), Net	(6)
Provision for income taxes	(1)
Net Income (Loss)	$ (5)

[1] In 2018, deferred tax activity incurred in other comprehensive income was offset by a valuation allowance.