Stock-Based Compensation - RSU, RS, Performance Shares (Details) - USD ($)	12 Months Ended
Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Restricted Stock Units and Restricted Stock
Unit and Shares Activity:
Number of Awards - Nonvested - Beginning balance	2,185,046	2,441,088	2,817,786
Number of Awards - Granted - Annual	604,256	749,068	671,204
Number of Awards - Granted - Other	20,692	8,115	26,886
Number of Awards - Vested	(769,598)	(960,345)	(1,010,612)
Number of Awards - Forfeited	(46,590)	(52,880)	(64,176)
Number of Awards - Nonvested - Ending balance	1,993,806	2,185,046	2,441,088
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	$ 127.47	$ 104.41
Weighted Average Grant Date Fair Value - Granted - Annual	176.10	148.20	165.86
Weighted Average Grant Date Fair Value - Granted - Other	233.77	169.00	156.94
Weighted Average Grant Date Fair Value - Vested	127.21	101.64	89.99
Weighted Average Grant Date Fair Value - Forfeited	158.25	145.95	118.99
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 162.60	$ 145.64	$ 127.47
Compensation expense yet to be recognized	$ 78,000,000
Expense recognition period	22 months
Fair value that vested	$ 136,000,000	$ 149,000,000	$ 166,000,000
Tax benefit realized from vesting	$ 45,000,000	$ 56,000,000	$ 62,000,000
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	871,192	1,099,752
Number of Awards - Granted - Annual	201,261	219,431	227,798
Number of Awards - Vested	(313,942)	(367,428)	(323,938)
Number of Awards - Performance Change	154,774	(37,534)	(106,760)
Number of Awards - Forfeited	(12,498)	(29,383)	(25,660)
Number of Awards - Nonvested - Ending balance	685,873	656,278	871,192
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	$ 120.89	$ 102.65
Weighted Average Grant Date Fair Value - Granted - Annual	191.28	160.17	158.88
Weighted Average Grant Date Fair Value - Vested	124.88	99.06	83.08
Weighted Average Grant Date Fair Value - Performance Change	173.91	155.98	127.70
Weighted Average Grant Date Fair Value - Forfeited	171.36	149.08	125.33
Weighted Average Grant Date Fair Value - Nonvested - Ending balance	$ 171.90	$ 142.98	$ 120.89
Compensation expense yet to be recognized	$ 25,000,000
Expense recognition period	11 months
Fair value that vested	$ 55,000,000	$ 54,000,000	$ 54,000,000
Tax benefit realized from vesting	$ 15,000,000	$ 15,000,000	$ 15,000,000
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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