Other Postretirement Employee Benefit Plans (Narrative) (Details) - Other postretirement benefits - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Defined Benefit Plan Disclosure [Line Items]
Postretirement liability, noncurrent	$ (133)	$ (123)
Projected benefit obligation	148	139
Accumulated benefit obligation	$ 148	$ 139
Medical trend rate - initial	5.50%	5.70%
Medical trend rate - ultimate	4.50%	4.50%
Unrecognized prior service credits, before tax	$ (14)
Prior service credit, after tax	(11)
Unrecognized actuarial losses, net of tax	(27)
Unrecognized actuarial losses, net of tax	$ (21)