Stock-Based Compensation (Narrative) (Details) - USD ($) $ / shares in Units, shares in Millions, $ 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]
Number of shares available for grant (in shares)	53.9
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	2 years
Weighted average grant date fair value (in dollars per share)	$ 137.33	$ 112.09	$ 71.63
Shares issued in period (in shares)	1.1	1.2	0.9
Shares expected to be issued (in shares)	0.8
Total compensation cost not yet recognized	$ 77.3
Period for recognition of the compensation cost not yet recognized	12 months
Shareholder Value Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Weighted average grant date fair value (in dollars per share)	$ 139.14	$ 95.01	$ 48.51
Shares issued in period (in shares)	0.8	1.0	0.7
Shares expected to be issued (in shares)	1.0
Total compensation cost not yet recognized	$ 48.8
Period for recognition of the compensation cost not yet recognized	20 months
Relative Value Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Weighted average grant date fair value (in dollars per share)	$ 179.90
Total compensation cost not yet recognized	$ 13.7
Period for recognition of the compensation cost not yet recognized	24 months
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period	3 years
Weighted average grant date fair value (in dollars per share)	$ 135.42	$ 108.43	$ 70.95
Shares issued in period (in shares)	0.6	0.8	1.0
Shares expected to be issued (in shares)	0.6
Total compensation cost not yet recognized	$ 179.2
Period for recognition of the compensation cost not yet recognized	31 months
Grants in period (in shares)	1.1	1.5	1.3

The number of shares expected to be issued in the next twelve months under the plan.

No definition available.

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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

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- Definition

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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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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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-URI http://asc.fasb.org/extlink&oid=120381028&loc=d3e5070-113901

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- Definition

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).

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
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-Paragraph 2
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- Definition

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).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
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- Definition

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 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

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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Number of shares issued under share-based payment arrangement.

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