Pension Benefits Change in Assumptions (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Retirement Benefits [Abstract]
Defined Benefit Plan, Change in Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Decrease	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Net Periodic Benefit Cost, Discount Rate Decrease	$ 8
Defined Benefit Plan, Change in Assumptions Used Calculating Benefit Obligation, Discount Rate Decrease	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Benefit Obligation, Discount Rate Decrease	$ 101
Defined Benefit Plan, Change in Assumptions Used Calculating Net Periodic Benefit Cost, Discount Rate Increase	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Net Periodic Benefit Cost, Discount Rate Increase	$ (7)
Defined Benefit Plan, Change in Assumptions Used Calculating Benefit Obligation, Discount Rate Increase	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Benefit Obligation, Discount Rate Increase	$ (94)
Defined Benefit Plan, Change in Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Decrease	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Decrease	$ 3
Defined Benefit Plan, Change in Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Increase	0.25%
Defined Benefit Plan, Effect of Change in Assumption Used Calculating Net Periodic Benefit Cost, Expected Long-term Return on Assets Increase	$ (3)