Stock-Based Compensation - Stock-Based Compensation Expense and Stock Option Fair Value Assumptions (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Stock-Based Compensation
Stock option expense	$ 1	$ 5	$ 3
Restricted stock and unit awards expense	77	89	96
Total stock-based compensation expense	78	94	99
Tax benefit	$ 13	$ 19	$ 38
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Dividend yield		1.10%
Weighted-average grant-date fair value per option (USD per share)		$ 112.98
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free average interest rate		2.60%
Volatility		21.80%
Expected life (years)		5 years 8 months 1 day
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free average interest rate		2.70%
Volatility		22.00%
Expected life (years)		6 years 26 days

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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

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

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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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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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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 noncash expense for option under share-based payment arrangement.

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