Share-Based Compensation Plans Share-Based Compensation - Activity - RSU, PSU, MSU, DSU (Details) - $ / shares	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Discount percent	2.00%	2.00%	3.00%
Shares (in thousands)
Nonvested, beginning balance (shares)	265,800
Granted (shares)	86,300
Forfeited (shares)	(7,600)
Vested (shares)	(108,700)
Nonvested, ending balance (shares)	235,800	265,800
Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning balance (in dollars per share)	$ 39.80
Granted (in dollars per share)	72.31	$ 55.85	$ 29.06
Forfeited (in dollars per share)	58.27
Vested (in dollars per share)	37.64
Nonvested, ending balance (in dollars per share)	$ 52.63	$ 39.80
Performance Shares Units PSU
Shares (in thousands)
Nonvested, beginning balance (shares)	671,200
Granted (shares)	177,000
Forfeited (shares)	(13,200)
Vested (shares)	(137,700)
Nonvested, ending balance (shares)	697,300	671,200
Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning balance (in dollars per share)	$ 37.26
Granted (in dollars per share)	73.49
Forfeited (in dollars per share)	60.31
Vested (in dollars per share)	29.17
Nonvested, ending balance (in dollars per share)	$ 47.74	$ 37.26
Market Share Units MSU
Shares (in thousands)
Nonvested, beginning balance (shares)	74,200
Vested (shares)	(74,200)
Nonvested, ending balance (shares)	0	74,200
Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning balance (in dollars per share)	$ 30.37
Vested (in dollars per share)	30.37	$ 30.37
Nonvested, ending balance (in dollars per share)	$ 0.00	$ 30.37
Deferred Stock Units
Shares (in thousands)
Nonvested, beginning balance (shares)	10,900
Granted (shares)	12,500
Vested (shares)	(10,900)
Nonvested, ending balance (shares)	12,500	10,900
Weighted-Average Grant Date Fair Value Per Share
Nonvested, beginning balance (in dollars per share)	$ 60.80
Granted (in dollars per share)	74.43
Vested (in dollars per share)	60.80
Nonvested, ending balance (in dollars per share)	$ 74.43	$ 60.80

The number of equity-based payment instruments, excluding stock (or unit) options, that were forfeited during the reporting period.

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 (c)(1)(iv)(3)
-URI http://asc.fasb.org/extlink&oid=109197908&loc=d3e5070-113901

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- Definition

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
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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
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-Paragraph 2
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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).

+ References

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-Publisher FASB
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- Definition

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.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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.

+ References

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-Publisher FASB
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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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-Publisher FASB
-Name Accounting Standards Codification
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- Definition

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.

+ References

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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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- Definition

The average discount rate applied to insurance contracts to determine future policy benefits to be paid to or on behalf of policyholders.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
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