Income Taxes - Components of Net Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets
Post-retirement and pension benefit costs	$ 978	$ 1,164
Net operating loss carryforwards	2,463	3,138
Other employee benefits	96	119
Other	554	604
Gross deferred tax assets	4,091	5,025
Less valuation allowance	(1,566)	(1,538)
Net deferred tax assets	2,525	3,487
Deferred tax liabilities
Property, plant and equipment, primarily due to depreciation differences	(3,941)	(3,882)
Goodwill and other intangible assets	(2,473)	(2,755)
Gross deferred tax liabilities	(6,414)	(6,637)
Net deferred tax liability	$ (3,889)	$ (3,150)

Amount of deferred tax liability attributable to taxable temporary differences.

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