Employee Benefit Plans, Pre-Tax Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Net (gain) loss reclassified into income:
Total changes in other comprehensive income (loss)	$ (80)	$ (234)	$ 49
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(105)	(204)	(8)
Prior service (cost) credit	(5)	0	7
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	74	41	65
Prior service credit	(19)	(19)	(18)
Curtailment and settlement loss	5	4	7
Total changes in other comprehensive income (loss)	(50)	(178)	53
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(23)	(41)	9
Prior service (cost) credit	0	(3)	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	0	(3)	(2)
Prior service credit	(7)	(9)	(11)
Curtailment and settlement loss	0	0	0
Total changes in other comprehensive income (loss)	$ (30)	$ (56)	$ (4)