Employment Benefit Plans Assumptions Used (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost			4.20%	3.80%	4.50%
Expected Long-term Rate of Return on Plan Assets - net cost			6.60%	6.60%	6.80%
Rate of Compensation Increase - net cost			3.80%	3.80%	3.80%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount Rate - benefit obligations			4.10%	4.20%
Rate of Compensation Increase - benefit obligations			3.30%	3.80%
Assumptions Sensitivity Analysis [Abstract]
Effect of 50 basis point decrease in discount rate			$ 1
Effect of 50 basis point increase in discount rate			(7)
Effect of 50 basis point decrease in rate of return on plan assets			11
Effect of 50 basis point increase in rate of return on plan assets			$ (11)
Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost			4.10%	3.70%	4.50%
Rate of Compensation Increase - net cost			3.80%	3.80%	3.80%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount Rate - benefit obligations			3.90%	4.10%
Rate of Compensation Increase - benefit obligations			3.30%	3.80%
Assumptions Sensitivity Analysis [Abstract]
Effect of 50 basis point decrease in discount rate			$ 0
Effect of 50 basis point increase in discount rate			$ 0
Defined Benefit Plan, Assumed Health Care Cost Trend Rates [Abstract]
Assumed health care cost trend rate for next year (participants over 65)	[1]		3.00%	3.00%	3.00%
Assumed health care cost trend rate for next year (participants under 65)			7.40%	7.70%	7.90%
Rate to which health care cost trend rate for participants under 65 is expected to decline and remain			4.40%	4.50%	4.50%
Year that the rate reaches the ultimate trend rate			2039	2038	2028
Effect of One Percentage Point Increase on Service and Interest Cost Components			$ 1
Effect of One Percentage Point Decrease on Service and Interest Cost Components			(1)
Effect of One Percentage Point Increase on Postretirement Benefit Obligation			17
Effect of One Percentage Point Decrease on Postretirement Benefit Obligation			$ (15)
Scenario, Forecast [Member] | Pension Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost		4.10%
Expected Long-term Rate of Return on Plan Assets - net cost		6.60%
Scenario, Forecast [Member] | Retiree Health and Welfare Benefits [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount Rate - net cost		3.90%

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