Stock-Based Compensation - RSU, RS, Performance Shares (Details) - USD ($) $ / shares in Units, $ in Millions	6 Months Ended
Jun. 30, 2017	Jun. 30, 2016
Restricted Stock and Restricted Stock Units
Unit and Shares Activity:
Number of Awards - Nonvested - Beginning balance	2,185,046
Number of Awards - Granted - Annual	604,256
Number of Awards - Granted - Other	1,547
Number of Awards - Vested	(758,403)
Number of Awards - Forfeited	(31,511)
Number of Awards - Nonvested - Ending balance	2,000,935
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	$ 145.64
Weighted Average Grant Date Fair Value - Granted - Annual	176.10
Weighted Average Grant Date Fair Value - Granted - Other	184.98
Weighted Average Grant Date Fair Value - Vested	126.75
Weighted Average Grant Date Fair Value - Forfeited	157.36
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 161.84
Compensation expense yet to be recognized	$ 112
Expense recognition period	24 months
Fair value that vested	$ 134	$ 136
Tax benefit realized from vesting	$ 44	51
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 Awards - Nonvested - Beginning balance	656,278
Number of Awards - Granted - Annual	187,480
Number of Awards - Vested	(312,173)
Number of Awards - Performance Change	65,216
Number of Awards - Forfeited	(9,275)
Number of Awards - Nonvested - Ending balance	587,526
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	$ 142.98
Weighted Average Grant Date Fair Value - Granted - Annual	189.81
Weighted Average Grant Date Fair Value - Vested	124.63
Weighted Average Grant Date Fair Value - Performance Change	173.25
Weighted Average Grant Date Fair Value - Forfeited	168.09
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 170.63
Compensation expense yet to be recognized	$ 42
Expense recognition period	11 months
Fair value that vested	$ 55	54
Tax benefit realized from vesting	$ 15	$ 15
Vesting or performance period	3 years
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%

The impact on basic earnings per share calculation for restricted stock unit dividends.

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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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The number of shares issuable under a share-based award plan pertaining to grants made during the period on other than stock option plans.

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The weighted average fair value at grant for nonvested share-based awards issued during the period on other than stock option plans, other than annual and performance shares.

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The increase or decrease in the number of equity-based payment instruments, excluding stock (or unit) options, attributable to performance change during the reporting period.

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The weighted average fair value as of the grant date of equity-based award plans other than stock (unit) option plans, increased or decreased for performance change during the reporting period.

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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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Unrecognized cost of unvested share-based compensation awards.

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Weighted average period over which unrecognized compensation is expected to be recognized for equity-based compensation plans, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the 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 which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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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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The weighted average fair value of nonvested awards on equity-based plans excluding option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, revenue or profit achievement stock award plan) for which the employer is contingently obligated to issue equity instruments or transfer assets to an employee who has not yet satisfied service or performance criteria necessary to gain title to proceeds from the sale of the award or underlying shares or units.

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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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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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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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