Employee Benefits - Amounts Recognized on Balance Sheet and Amounts Recognized in Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018
Amounts recognized on the balance sheet
Noncurrent liabilities	$ (17,952)	$ (18,599)
Pension
Amounts recognized on the balance sheet
Noncurrent assets	5	3
Current liabilities	(67)	(71)
Noncurrent liabilities	(1,735)	(1,683)
Total	(1,797)	(1,751)
Amounts recognized in Accumulated Other Comprehensive Income (Pre-tax)
Prior service cost (benefit)	524	585
Total	524	585
Health Care and Life
Amounts recognized on the balance sheet
Noncurrent assets	0	0
Current liabilities	(603)	(292)
Noncurrent liabilities	(14,323)	(14,897)
Total	(14,926)	(15,189)
Amounts recognized in Accumulated Other Comprehensive Income (Pre-tax)
Prior service cost (benefit)	(3,749)	(4,698)
Total	$ (3,749)	$ (4,698)

Amount, before tax, of accumulated other comprehensive (income) loss for defined benefit plan, that has not been recognized in net periodic benefit cost (credit).

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Amount of asset (liability), recognized in statement of financial position, for defined benefit pension and other postretirement plans.

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Amount, before tax, after reclassification adjustment, of (increase) decrease in accumulated other comprehensive income from prior service cost (credit) of defined benefit plan.

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Amount of asset, recognized in statement of financial position, for overfunded defined benefit pension and other postretirement plans.

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