STOCK INCENTIVE PLANS - Restricted Stock Units (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Weighted Average Price Per Share [Abstract]
RSU expense	$ 32	$ 27	$ 23
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of shares vested	$ 31	$ 19	$ 22
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested [Roll Forward]
Outstanding at beginning of period (in shares)	326,124	343,814	352,919
Issued (in shares)	140,815	96,823	141,775
Canceled (in shares)	(26,254)	(36,224)	(56,393)
Vested (in shares)	(123,271)	(78,289)	(94,487)
Outstanding at end of period (in shares)	317,414	326,124	343,814
Weighted Average Price Per Share [Abstract]
Outstanding at beginning of period, weighted average price per share (in dollars per share)	$ 259.88	$ 245.38	$ 226.31
Issued, weighted average price per share (in dollars per share)	252.11	299.25	284.98
Cancelled, weighted average price per share (in dollars per share)	257.56	253.22	245.08
Vested, weighted average price per share (in dollars per share)	252.05	247.96	233.75
Outstanding at end of period, weighted average price per share (in dollars per share)	$ 259.67	$ 259.88	$ 245.38
Unrecognized compensation	$ 41
Weighted average period to recognize (in years)	1 year 10 months 24 days
Minimum \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	1 year
Maximum \| Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	7 years

Share-Based Compensation Fair Value of Vested Restricted Stock Units

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

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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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Amount of noncash expense for award of restricted stock or unit under share-based payment arrangement.

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

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

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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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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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