Employee Benefit Plans, Pre-Tax Amounts in Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	$ 828	$ 894
Prior service credit	(108)	(121)
Total	720	773
Other Postretirement Benefit Plans [Member]
Pension and Other Postretirement Benefit Plans Accumulated Other Comprehensive Income (Loss), before Tax
Net actuarial (gain) loss	(64)	(57)
Prior service credit	(31)	(42)
Total	$ (95)	$ (99)