Retirement Plans (Narrative) (Details)		3 Months Ended					12 Months Ended
		Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Defined Benefit Plan Disclosure [Line Items]
Former Employees		45,000
Defined Benefit Plan, Plan Assets, Increase (Decrease) for Assets Transferred to (from) Plan		$ 1,300,000,000
Monthly Benefit Payments		450
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(376,000,000)
Years of eligibility to participate in pension plan							1
Age to participate in the pension plan							21
change in basis point for assumptions for next year							25.00%
Settlements					$ (1,200,000,000)
Defined contribution plan, cost recognized							$ 117,000,000	$ 106,000,000	$ 100,000,000
Payment for Pension Benefits							$ 1,250,000,000	750,000,000	750,000,000
Number of nonqualified pension plans							3
Number of SERP plans							2
Domestic Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		3,000,000	$ 3,000,000	$ 439,000,000			$ 383,000,000	445,000,000	$ 15,000,000
Defined Benefit Plan, Plan Assets, Benefits Paid							769,000,000	767,000,000
Settlements		(9,000,000)	$ (8,000,000)				$ (1,295,000,000)	$ (1,222,000,000)
Discount rate	[1]						4.03%	4.05%	4.10%
Expected long-term rate of return on plan assets							7.50%	7.75%	7.75%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost, Expected Long Term Return on Assets for Next Year							7.50%
Defined Benefit Plan, Assumptions Used Calculating Net Periodic Benefit Cost Discount Rate for Next Year							3.60%
Defined benefit expense							$ 717,000,000	$ 809,000,000	$ 461,000,000
Total recognized in other comprehensive income							(901,000,000)
Defined Benefit Plan Total Recognized in Net Periodic Benefit Cost and Other Comprehensive Income		(184,000,000)					(184,000,000)	626,000,000	505,000,000
Accumulated benefit obligation for defined benefit plans		13,200,000,000					13,200,000,000	13,500,000,000
Expected amortization of gain (loss), next fiscal year		327,000,000					327,000,000
Expected amortization of prior service cost (credit), next fiscal year		17,000,000					17,000,000
Projected benefit obligation		13,264,000,000					13,264,000,000	13,683,000,000
Defined benefit plan, net periodic benefit cost estimate for next fiscal year		167,000,000					$ 167,000,000
Rate of compensation increase							3.75%
Payment for Pension Benefits							$ 1,250,000,000	750,000,000	750,000,000
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		708,000,000					708,000,000
Defined benefit plan, Net periodic pension cost, special pension adjustments, curtailment charges and termination benefits							45,000,000
Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement							1,000,000	0	$ 0
Defined Benefit Plan, Plan Assets, Benefits Paid							8,000,000	9,000,000
Settlements							$ (4,000,000)	$ (2,000,000)
Discount rate	[1]						3.88%	4.72%	4.72%
Expected long-term rate of return on plan assets							6.73%	6.55%	6.64%
Defined benefit expense							$ 5,000,000	$ 4,000,000	$ 6,000,000
Total recognized in other comprehensive income							5,000,000
Defined Benefit Plan Total Recognized in Net Periodic Benefit Cost and Other Comprehensive Income		10,000,000					10,000,000	23,000,000	$ 8,000,000
Accumulated benefit obligation for defined benefit plans		230,000,000					230,000,000	205,000,000
Projected benefit obligation		215,000,000					215,000,000	190,000,000
Supplemental Employee Retirement Plan, Defined Benefit [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Net Periodic Benefit Cost (Credit), Gain (Loss) Due to Settlement		(7,000,000)
Defined Benefit Plan, Plan Assets, Benefits Paid						$ 62,000,000	40,000,000	$ 21,000,000
Defined Benefit Plan, Expected Future Benefit Payment, Next Twelve Months		$ 30,000,000					$ 30,000,000

[1] Represents the weighted average rate for the U.S. qualified plans in 2017 and 2016 due to the remeasurements