Pension Plans, Postretirement and Other Employee Benefits - Healthcare Trend (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Initial health care cost trend rate	6.90%	6.80%	7.00%
Ultimate health care cost trend rate	4.90%	4.50%	4.50%
Other Postretirement Benefits Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
100 basis point (bp) increase in health care cost trend rate	$ 23
100 bp decrease in health care cost trend rate	(20)
Maximum | Other Postretirement Benefits Plans
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
100 basis point (bp) increase in health care cost trend rate, Total Interest and Service Costs	1
100 bp decrease in health care cost trend rate, Total Interest and Service Costs	$ (1)