Stock-based Compensation (Narrative) (Details) $ in Millions	3 Months Ended
Mar. 31, 2021 USD ($)
Stock Options [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Contractual term	10 years
Years until vest	3 years
Stock options, subject to performance or market-based vesting conditions	None
Unrecognized compensation expense	$ 27
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 8 months 12 days
Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Years until vest	4 years
Unrecognized compensation expense	$ 129
Expected weighted average period (in years) of nonvested stock options to be recognized	2 years 2 months 12 days
Performance Retention Awards [Member]
Schedule of Share-based Compensation Arrangements [Line Items]
Requisite service period	37 months
Contractual terms of award	We expense two-thirds of the fair value of the units that are probable of being earned based on our forecasted ROIC over the 3-year performance period, and with respect to the third year of the plan, the remaining one-third of the fair value is subject to the relative three-year OIG.
ROIC performance period	3 years
Unrecognized compensation expense	$ 34
Expected weighted average period (in years) of nonvested stock options to be recognized	1 year 10 months 24 days

Performance period in which ROIC is evaluated in determining equity-based compensation awards received.

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The number of stock options outstanding that are subject to performance or market-based vesting conditions before giving the employee the legal right to convert the award to shares.

+ References

No definition available.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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-Topic 718
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Weighted-average period over which cost not yet recognized is expected to be recognized for award under share-based payment arrangement, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days.

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Estimated period over which an employee is required to provide service in exchange for the equity-based payment award, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Period over which grantee's right to exercise award under share-based payment arrangement is no longer contingent on satisfaction of service or performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. Includes, but is not limited to, combination of market, performance or service condition.

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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Description of terms of award under share-based payment arrangement.

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Period from grant date that an equity-based award expires, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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