Retirement Plans (Retirement Plans, Net Periodic Benefit Cost, Assumptions, and Expected Cash Flows) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	$ 17
Defined Benefit Plan, Net Periodic Benefit Cost (Credit) [Abstract]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit)	30	$ 30	$ 42
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement and Curtailment	13	$ 8
Defined Benefit Plan, Estimated Future Benefit Payments [Abstract]
Defined Benefit Plan, Estimated Future Employer Contributions in Next Fiscal Year	17
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months	68
Defined Benefit Plan, Expected Future Benefit Payment, Year Two	61
Defined Benefit Plan, Expected Future Benefit Payment, Year Three	63
Defined Benefit Plan, Expected Future Benefit Payment, Year Four	67
Defined Benefit Plan, Expected Future Benefit Payment, Year Five	72
Defined Benefit Plan, Expected Future Benefit Payment, Five Fiscal Years Thereafter	$ 424
Foreign Plan [Member]
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Benefit Obligation [Abstract]
Discount rate	2.80%	2.90%
Rate of compensation increase	5.50%	4.80%
Defined Benefit Plan, Weighted Average Assumptions Used in Calculating Net Periodic Benefit Cost [Abstract]
Discount rate	2.90%	4.20%	4.10%
Expected long-term return on plan assets	4.20%	5.30%	5.90%
Rate of compensation increase	4.80%	5.40%	5.30%