Stock-Based Compensation - RSU, RS, Performance Shares (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended
Mar. 31, 2021	Mar. 31, 2020
Restricted Stock and Restricted Stock Units
Unit and Shares Activity:
Number of Shares - Nonvested - Beginning balance	1,722,000
Number of Shares - Granted - Annual	721,000
Number of Shares - Vested	(433,000)
Number of Shares - Forfeited	(33,000)
Number of Shares - Nonvested - Ending balance	1,977,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures
Weighted Average Grant Date Fair Value - Nonvested - Beginning balance	$ 189.78
Weighted Average Grant Date Fair Value - Granted - Annual	175.09
Weighted Average Grant Date Fair Value - Vested	232.62
Weighted Average Grant Date Fair Value - Forfeited	173.54
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 175.31
Compensation expense yet to be recognized	$ 141
Expense recognition period	27 months
Fair value that vested	$ 78	$ 88
Tax benefit realized from vesting	$ 14	16
Vesting or performance period	3 years
Value of dividend equivalents for restricted stock units that are forfeited	$ 0
Impact on basic earnings per share due to restricted stock units dividends	$ 0
Performance Shares
Unit and Shares Activity:
Number of Shares - Nonvested - Beginning balance	423,000
Number of Shares - Granted - Annual	163,000
Number of Shares - Distributed	(115,000)
Number of Shares - Performance Change	17,000
Number of Shares - Forfeited	(4,000)
Number of Shares - Nonvested - Ending balance	484,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures
Weighted Average Grant Date Fair Value - Nonvested - Beginning balance	$ 188.61
Weighted Average Grant Date Fair Value - Granted - Annual	$ 176.41
Weighted Average Grant Date Fair Value - Distributed	228.80
Weighted Average Grant Date Fair Value - Performance Change	$ 178.43
Weighted Average Grant Date Fair Value - Forfeited	172.92
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 174.75
Compensation expense yet to be recognized	$ 40
Expense recognition period	21 months
Fair value that vested	$ 22	35
Tax benefit realized from vesting	$ 4	$ 7
Vesting or performance period	3 years
Performance shares awarded at estimated number of shares at the end of the performance period	100.00%
Performance Shares \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures
Expense recognition period	3 years
Number of shares to be delivered based on percent of each performance share granted upon satisfaction of performance conditions	200.00%
Performance Shares \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures
Expense recognition period	1 year
Number of shares to be delivered based on percent of each performance share granted upon satisfaction of performance conditions	0.00%

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Number of shares that are delivered at the end of the three-year performance period that may be anywhere from zero to two hundred percent of the performance shares granted.

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Amount of increase (decrease) in additional paid in capital (APIC) resulting from a tax benefit (deficiency) associated with an share-based compensation plan other than an employee stock ownership plan (ESOP).

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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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The value of dividends forfeited related to restricted stock awards forfeited.

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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 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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Fair value of share-based awards for which the grantee gained the right by satisfying service and performance requirements, to receive or retain shares or units, other instruments, or cash.

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