Stock-Based Compensation Plans - Nonqualified Stock Options, Assumptions and Other Disclosures (Details) - Nonqualified Stock Options - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Assumptions used to estimate fair value of stock options granted during period
Weighted-average expected volatility (as a percent)	26.00%	27.60%	31.70%
Weighted-average expected term	7 years	7 years	6 years 6 months
Weighted-average risk-free interest rate (as a percent)	2.80%	2.20%	1.50%
Weighted-average expected dividend yield (as a percent)	3.19%	2.87%	4.07%
Weighted-average estimated fair value of stock options granted (in dollars per share)	$ 14.85	$ 15.31	$ 8.91
Other nonqualified stock option disclosures
Unrecognized compensation costs	$ 1.6
Weighted-average service period over which unrecognized compensation costs will be recognized	1 year 9 months 18 days
Cash received from stock options exercised	$ 29.0	$ 133.9	$ 15.3
Tax benefits realized for the tax deductions from options exercised	$ 3.9	$ 18.1	$ 9.0

No definition available.

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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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Amount of tax benefit from exercise of stock options granted under share-based compensation arrangement.

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Amount of cash inflow from exercise of stock options granted under share-based compensation arrangement.

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No definition available.

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- Definition

The estimated dividend rate (a percentage of the share price) to be paid (expected dividends) to holders of the underlying shares over the option's term.

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The estimated measure of the percentage by which a share price is expected to fluctuate during a period. Volatility also may be defined as a probability-weighted measure of the dispersion of returns about the mean. The volatility of a share price is the standard deviation of the continuously compounded rates of return on the share over a specified period. That is the same as the standard deviation of the differences in the natural logarithms of the stock prices plus dividends, if any, over the period.

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The risk-free interest rate assumption that is used in valuing an option on its own shares.

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- Definition

The weighted average grant-date fair value of options granted during the reporting period as calculated by applying the disclosed option pricing methodology.

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Expected term of share-based compensation awards, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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