Reclassifications from Accumulated Other Comprehensive Income (Loss) (Amounts Reclassified from Accumulated Other Comprehensive Income (Loss)) (Details) - USD ($) $ in Millions	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income (Loss), Net	$ (1)			$ 2			$ (1)	$ 3
Provision (Benefit) for Income Taxes	0			0			0	406
Net Income	$ (1,857)	$ (609)	$ 80	$ (593)	$ (880)	$ (1,547)	(2,386)	$ (3,020)
Amount Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net Income							4
Amortization of prior service cost and net loss | Amount Reclassified from Accumulated Other Comprehensive Income
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other Income (Loss), Net							5
Provision (Benefit) for Income Taxes							1
Net Income							$ 4