Employee Benefit Plans, Pre-Tax Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Net (gain) loss reclassified into income:
Total changes in other comprehensive income (loss)	$ (234)	$ 49	$ (65)
Pension Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(204)	(8)	(73)
Prior service (cost) credit	0	7	(4)
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	41	65	53
Prior service credit	(19)	(18)	(20)
Curtailment and settlement loss	4	7	4
Total changes in other comprehensive income (loss)	(178)	53	(40)
Other Postretirement Benefit Plans [Member]
Net gain (loss) arising during the year:
Net actuarial gain (loss)	(41)	9	(6)
Prior service (cost) credit	(3)	0	0
Net (gain) loss reclassified into income:
Net actuarial (gain) loss	(3)	(2)	(3)
Prior service credit	(9)	(11)	(16)
Curtailment and settlement loss	0	0	0
Total changes in other comprehensive income (loss)	$ (56)	$ (4)	$ (25)