Restructuring Costs - Activity Related to Expenses Incurred and Cash Payments Made (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
Dec. 31, 2020	Dec. 31, 2020
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	$ 0
Expenses Incurred	1,060	$ 1,060
Cash Payments	(738)
Adjustments	(159)
Restructuring Reserve, Ending Balance	163	163
Contract termination costs
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	0
Expenses Incurred	178	178
Cash Payments	(96)
Adjustments	(1)
Restructuring Reserve, Ending Balance	81	81
Severance costs
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	0
Expenses Incurred	385	385
Cash Payments	(239)
Adjustments	(94)
Restructuring Reserve, Ending Balance	52	52
Network decommissioning
Restructuring Reserve [Roll Forward]
Restructuring Reserve, Beginning Balance	0
Expenses Incurred	497	497
Cash Payments	(403)
Adjustments	(64)
Restructuring Reserve, Ending Balance	$ 30	$ 30

Amount of cash payments made as the result of exit or disposal activities. Excludes payments associated with a discontinued operation or an asset retirement obligation.

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-Publisher FASB
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- Definition

Amount of expenses associated with exit or disposal activities pursuant to an authorized plan. Excludes expenses related to a discontinued operation or an asset retirement obligation.

+ References

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- Definition

Carrying amount (including both current and noncurrent portions of the accrual) as of the balance sheet date pertaining to a specified type of cost associated with exit from or disposal of business activities or restructuring pursuant to a duly authorized plan.

+ References

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- Definition

Amount of expense (reversal of expense) which increases (decreases) the restructuring reserve from an adjustment to a previously accrued restructuring liability.

+ References

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- Definition

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

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