Employee Benefit Plans, Pre-Tax Amounts in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Pension Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	$ 988	$ 828
Prior service credit	(90)	(108)
Total	898	720
Other Postretirement Benefit Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	(20)	(64)
Prior service credit	(19)	(31)
Total	$ (39)	$ (95)