Employment Benefit Plans Assumptions Used (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost		4.20%	3.60%	4.10%
Expected Long-term Rate of Return on Plan Assets - net cost		6.70%	6.60%	6.60%
Rate of Compensation Increase - net cost		3.50%	3.60%	3.30%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount Rate - benefit obligations		3.20%	4.20%
Rate of Compensation Increase - benefit obligations		3.10%	3.50%
Assumptions Sensitivity Analysis [Abstract]
Effect of 50 basis point decrease in discount rate		$ 5
Effect of 50 basis point increase in discount rate		2
Effect of 50 basis point decrease in rate of return on plan assets		13
Effect of 50 basis point increase in rate of return on plan assets		$ (13)
Forecast | Pension Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost	3.20%
Expected Long-term Rate of Return on Plan Assets - net cost	6.70%
Forecast | Retiree Health and Welfare Benefits
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost	3.10%