Fair Value of Financial Instruments (Details) - Fair Value Measurements Determined on a Nonrecurring Basis - Fair Value Inputs, Level 2 - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Carrying Amount
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	$ 30,848	$ 31,542
Interest rate swap contracts (see Note 10)	67	107
Fair Value
Fair value disclosure
Long-term debt, excluding finance lease and other obligations	32,085	33,217
Interest rate swap contracts (see Note 10)	$ 67	$ 107

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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