Benefit Obligations (Plan Assets Narrative) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets		7.30%	7.80%	8.20%
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 20
United States Pension Plan of US Entity [Member]
Defined Benefit Plan Disclosure [Line Items]
Actual return on plan assets		6.90%
Expected return on plan assets		7.50%	8.00%	8.50%
Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 4
Nonqualified Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Estimated Future Employer Contributions in Next Fiscal Year		$ 22
Scenario, Forecast [Member] | United States Pension Plan of US Entity [Member]
Defined Benefit Plan Disclosure [Line Items]
Expected return on plan assets	7.50%