AOCL (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	$ (1,686)	$ (1,642)	$ (1,770)
Other Comprehensive Income (Loss), Net of Tax	(84)	(23)
Accumulated Foreign Currency Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(55)	(53)	(55)	$ (56)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	0	3
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive loss	(1,631)	(1,589)	$ (1,715)	$ (1,609)
Other Comprehensive Income (Loss), before Reclassifications, Net of Tax	67	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax	22	26
Reclassification from AOCI, Current Period, Tax	(5)	(6)
Other Comprehensive Income (Loss), Net of Tax	84	20
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	17	20
Other Comprehensive Income (Loss), before Reclassifications, before Tax	87	0
Other Comprehensive Income (Loss) before Reclassifications, Tax	$ (20)	$ 0