Share-Based Compensation Plans - Summary of Restricted Stock Activity (Details) - Restricted Stock - USD ($) $ / shares in Units, shares in Thousands, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2016
Shares
Unvested at beginning of period (in shares)	446	396	448
Granted (in shares)	200	236	145
Vested (in shares)	(145)	(150)	(174)
Forfeited (in shares)	(17)	(36)	(23)
Unvested at end of period (in shares)	484	446	396
Wtd. Avg. Price Per Share
Unvested at beginning of period (in dollars per share)	$ 97	$ 92	$ 77
Granted (in dollars per share)	92	84	119
Vested (in dollars per share)	95	76	77
Forfeited (in dollars per share)	93	93	89
Unvested at end of period (in dollars per share)	$ 94	$ 97	$ 92
Equity Other Than Options, Additional [Abstract]
Unvested (in years)	1 year 4 months 24 days	1 year 6 months	1 year 3 months 18 days	1 year 2 months 12 days
Unvested, aggregate intrinsic value	$ 44

No definition available.

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The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 10
-Section 50
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- Definition

Weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans that were not exercised or put into effect as a result of the occurrence of a terminating event.

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-Publisher FASB
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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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- Definition

The number of non-vested equity-based payment instruments, excluding stock (or unit) options, that validly exist and are outstanding as of the balance sheet date.

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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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No definition available.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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-Publisher FASB
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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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No definition available.

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Weighted average remaining contractual term for equity-based awards excluding options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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The number of equity-based payment instruments, excluding stock (or unit) options, that vested during the reporting period.

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

The weighted average fair value as of grant date pertaining to an equity-based award plan other than a stock (or unit) option plan for which the grantee gained the right during the reporting period, by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash in accordance with the terms of the arrangement.

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Intrinsic value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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No definition available.

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