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Stock-Based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Millions | 12 Months Ended
--- | ---
Dec. 31, 2020 | Dec. 31, 2019 | Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Available for future grants (in shares) | 8,995,582 |  |
Amended LTIP plan-award granted as an option or stock appreciation right (in shares) | 1 |  |
Amended LTIP plan - award granted in a form other than option or stock appreciation right (in shares) | 1.61 |  |
Aggregate intrinsic value of options outstanding | $ 213 |  |
Weighted average remaining contractual term of options outstanding | 4 years 7 months 6 days |  |
Number of shares exercisable (in shares) | 1,220,685 |  |
Aggregate intrinsic value of options exercisable | $ 183 |  |
Exercisable weighted average exercise price (in dollars per share) | $ 87.75 |  |
Weighted average remaining contractual term of options exercisable | 2 years 10 months 24 days |  |
Unrecognized compensation related to stock options granted | $ 5 |  |
LTIP |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Maximum number of shares available for grant (in shares) | 104,125,000 |  |
Available for future grants (in shares) | 8,995,582 | 9,294,726 | 8,644,108
LTIP dividend equivalent payment, in years | 4 years |  |
Dividend yield for period dividend equivalents paid | 1.76% | 2.06% | 1.94%
Unrecognized compensation related to stock options granted | $ 1 |  |
Unrecognized compensation, weighted average period of recognition | 2 years 4 months 24 days |  |
LTIP options during vesting period |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Dividend yield for period dividend equivalents paid | 0.00% |  |
TSOP |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Maximum number of shares available for grant (in shares) | 6,000,000 |  |
Available for future grants (in shares) | 435,699 | 434,401 | 422,973
Restricted Stock Units (RSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Unrecognized compensation related to stock options granted | $ 29 |  |
Unrecognized compensation, weighted average period of recognition | 2 years 4 months 24 days |  |
Performance Share Units (PSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Unrecognized compensation, weighted average period of recognition | 1 year 8 months 12 days |  |
PSU Cycle | 3 years |  |
Grant Date, 2019 | Restricted Stock Units (RSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting period (in years) | 4 years |  |
Grant Date, 2018 | Restricted Stock Units (RSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting period (in years) | 4 years |  |
Grant Date, 2017 | Restricted Stock Units (RSUs) |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting period (in years) | 5 years |  |
Minimum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Vesting period (in years) | 1 year |  |
Maximum |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Expiration period (in years) | 10 years |  |

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- Definition Amount of cost not yet recognized for nonvested award under share-based payment arrangement. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (i) -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901 + Details
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