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Share-Based Payments - Market Stock Units Activity (Details) - Market stock units - $ / shares shares in Thousands		12 Months Ended
		Dec. 31, 2020		Dec. 31, 2019	Dec. 31, 2018
Shares
Beginning balance, unvested shares (in shares)		183
Granted (in shares)	[1]	133
Vested (in shares)		(82)
Forfeited (in shares)		(33)
Ending balance, unvested shares (in shares)		201		183
Weighted Average Grant Date Fair Value
Beginning balance, weighted average grant date fair value (in dollars per share)		$ 378.09
Granted (in dollars per share)		398.61	[1]	$ 378.08	$ 378.85
Vested (in dollars per share)		375.42
Forfeited (in dollars per share)		402.62
Ending balance, weighted average grant date fair value (in dollars per share)		$ 388.98		$ 378.09
[1] MSUs granted during 2020 include awards granted in conjunction with our annual awards made in February 2020 and MSUs granted in conjunction with the hiring of employees. These grants reflect the target number of shares eligible to be earned at the time of grant. MSUs granted in 2020 also reflect an adjustment based upon the final performance multiplier in relation to shares granted in 2019, 2018 and 2017.

X

- Definition

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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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 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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