Basis of Presentation (Unaudited) (Details 4) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Jan. 01, 2016
Accumulated Other Comprehensive Loss
Unamortized benefit plan costs, net of tax benefit of $1,968 for 2018 and $3,056 for 2017	$ (5,560)	$ (4,586)
Cumulative translation adjustment	(138)	(136)
Other, net	(1)	4
Total accumulated other comprehensive loss	(5,699)	(4,718)
Unamortized benefit plan costs - Tax Benefit (expense)	1,968	3,056
Unamortized benefit plan costs, net actuarial losses, after-tax	5,700	4,700
Unamortized benefit plan costs, reclassified from other comprehensive income to net earnings	$ 86	99
Restatement Adjustment [Member] | Accounting Standards Update 2018-02 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect Of New Accounting Principle In Period Of Adoption			$ 1,100
Tax Cuts and Job Act, Income Tax Expense (Benefit)			73
Restatement Adjustment [Member] | Accounting Standards Update 2016-01 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect Of New Accounting Principle In Period Of Adoption			$ 4
Restatement Adjustment [Member] | Accounting Standards Update 2014-09 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative Effect Of New Accounting Principle In Period Of Adoption				$ 148
Accumulated Other Comprehensive Loss
Total accumulated other comprehensive loss		$ 0