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Employee Stock and Incentive Plans - Performance Shares and Restricted Stock Units (Details) - USD ($)
$ / shares in Units, $ in Millions

1 Months Ended

12 Months Ended

Feb. 29, 2020

Jan. 31, 2020

Dec. 31, 2019

Dec. 31, 2018

Dec. 31, 2017

Performance Shares [Member]

Stock-based Compensation [Line Items]

Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition

1 year 7 months 6 days

Number of Shares [Rollforward]

As of January 1

99,585

129,693

127,898

127,580

Granted

^[1]

60,747

66,557

50,729

Awarded

(75,943)

(58,293)

0

Unearned Grant Award

0

0

(40,801)

Forfeited

(14,912)

(6,469)

(9,610)

As of December 31

99,585

129,693

127,898

Performance Period (Years)

3 years

Weighted-Average Grant Date Fair Value [Abstract]

As of January 1

$ 72.78

$ 66.12

$ 58.23

$ 52.56

Granted

^[1]

63.89

76.42

62.90

Awarded

53.44

59.82

0

Unearned Grant Award

0

0

46.27

Forfeited

77.14

72.99

58.29

As of December 31

$ 72.78

$ 66.12

$ 58.23

Restricted Stock Units [Member]

Number of Shares [Rollforward]

As of January 1

39,943

49,771

55,248

54,728

Granted

^[2]

13,927

16,573

21,241

Awarded

(21,110)

(18,881)

(17,281)

Forfeited

(2,645)

(3,169)

(3,440)

As of December 31

39,943

49,771

55,248

Performance Period (Years)

3 years

Weighted-Average Grant Date Fair Value [Abstract]

As of January 1

$ 69.30

$ 60.74

$ 56.18

$ 51.79

Granted

^[2]

74.93

71.11

62.20

Awarded

52.44

55.78

49.72

Forfeited

72.43

64.92

56.00

As of December 31

$ 69.30

$ 60.74

$ 56.18

Subsequent Event [Member] | Performance Shares [Member]

Number of Shares [Rollforward]

Granted

22,000

Awarded

(25,000)

Performance Period (Years)

3 years

Granted, Grant Date Fair Value

$ 1.8

Awarded, Grant Date Fair Value

$ 1.6

Subsequent Event [Member] | Restricted Stock Units [Member]

Number of Shares [Rollforward]

Granted

14,000

Awarded

(15,000)

Granted, Grant Date Fair Value

$ 1.1

Awarded, Grant Date Fair Value

$ 0.9

[1]	Shares granted include accrued dividends.
[2]	Shares granted include accrued dividends.

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- Definition

The total grant date fair value of equity-based awards other than options, granted during the period.

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