Fair Value of Financial Instruments - Carrying Amount and Fair Value of Debt (Details) - Fair value measurements determined on a nonrecurring basis - Level 2 - USD ($) $ in Millions	Dec. 31, 2021	Dec. 31, 2020
Carrying Amount
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	$ 28,635	$ 31,542
Interest rate swap contracts	25	107
Carrying Amount \| Disposal Group, Held-for-sale, Not Discontinued Operations
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	1,400
Fair Value
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	29,221	33,217
Interest rate swap contracts	25	$ 107
Fair Value \| Disposal Group, Held-for-sale, Not Discontinued Operations
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	$ 1,600

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

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