Stock-Based Compensation - Stock Options and Appreciation Rights, fair value (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value
Weighted average Black-Scholes fair value of stop options and SARs granted (in usd per share)	$ 203.51	$ 102.41	$ 156.86	$ 78.78
Additional disclosures:
Aggregate intrinsic value, outstanding	$ 673		$ 673
Remaining term, outstanding (in years)			7 years 10 months 24 days
Aggregate intrinsic value, exercisable	$ 212		$ 212
Remaining term, exercisable (in years)			7 years
Aggregate intrinsic value, stock options and vesting RSA's			$ 381	$ 164
Stock options
Fair Value
Risk-free interest rate, minimum	0.60%	0.20%	0.50%	0.20%
Risk-free interest rate, maximum	0.90%	0.40%	1.10%	1.50%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Volatility, minimum	126.40%	135.40%	124.70%	116.00%
Volatility, maximum	140.00%	152.20%	142.00%	152.20%
Stock options \| Minimum
Fair Value
Expected term (in years)	4 years 1 month 6 days	4 years	4 years 1 month 6 days	4 years
Stock options \| Maximum
Fair Value
Expected term (in years)	6 years 1 month 6 days	5 years 3 months 18 days	6 years 1 month 6 days	7 years 7 months 6 days

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the maximum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The estimated measure of the minimum percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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The minimum risk-free interest rate assumption that is used in valuing an option on its own shares.

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Amount of accumulated difference between fair value of underlying shares on dates of exercise and exercise price on options exercised (or share units converted) into shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Expected term of 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 difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term for vested portions of options outstanding and currently exercisable or convertible, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Weighted average remaining contractual term for option awards outstanding, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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