Pension and Other Postretirement Benefits, Net Loss and Prior Service Cost Balances in Accumulated Other Comprehensive Loss (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	$ 958	$ 1,035
Prior service cost (credit)	(1)	10
Total amount recognized	957	1,045
Postretirement Benefit Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Net loss (gain)	(3)	(3)
Prior service cost (credit)	(25)	(27)
Total amount recognized	$ (28)	$ (30)