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Other Postretirement Employee Benefit Plans (Narrative) (Details) - Other postretirement benefits - USD ($)
$ in Millions
Dec. 31, 2019
Dec. 31, 2018
Defined Benefit Plan Disclosure [Line Items]    
Postretirement liability, noncurrent $ (123) $ (129)
Medical trend rate - initial 5.70% 6.00%
Medical trend rate - ultimate 4.50% 4.50%
Unrecognized prior service credits, before tax $ (16)  
Unrecognized net prior service credits, net of tax (12)  
Unrecognized actuarial losses, before tax (13)  
Unrecognized actuarial losses, net of tax (9)  
Future amortization of prior service cost (credit) (2)  
Future amortization of prior service cost (credit), net of tax $ (2)