Stock-Based Compensation (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options Outstanding, Weighted-Average Remaining Contractual Term	4 years 10 months 24 days
Options Outstanding, Aggregate Intrinsic Value	$ 52.0
Maximum number of shares reserved for grant awards under the plan	13,900,000
Number of shares counted against reserve for determining number of shares of stock available for grant under the Plan for each option	1
Number of shares counted against reserve for each share of stock granted, other than option or stock appreciation right	1.61
Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant	7,200,000
Maximum number of underlying shares that may be granted to a participant in any one calendar year	5,000,000.0
Period over which maximum award grant per participant applies	1 year
Stock options, shares
Exercised (in shares)	(629,186)	(462,647)	(90,938)
Selected amounts pertaining to stock option exercises:
Issuances of common stock under employee stock plans	$ 19.0	$ 12.0	$ 1.0
Stock-based compensation costs
Stock-based compensation expense	28.0	21.0	17.0
Income tax benefit	(6.0)	(4.0)	(6.0)
Stock-based compensation expense, net of income taxes	$ 22.0	$ 17.0	$ 11.0
Options Exercisable, Weighted-Average Remaining Contractual Term	4 years 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value	$ 43.0
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Contractual life	10 years
Weighted-average assumptions:
Weighted-average expected volatility (as a percent)			40.00%
Expected term of stock options			4 years 3 months 18 days
Risk-free interest rate (as a percent)			1.90%
Weighted-average expected dividend yield (as a percent)			3.90%
Weighted-average grant date fair value per share of options granted (in dollars per share)			$ 7.66
Stock options, shares
Outstanding at the beginning of the period (in shares)	5,784,100
Exercised (in shares)	(629,186)
Forfeited (in shares)	(54,045)
Expired (in shares)	(40,977)
Outstanding at the end of the period (in shares)	5,059,892	5,784,100
Exercisable balance at the end of the period (in shares)	4,518,530
Stock option activity, weighted-average exercise price
Outstanding at the beginning of the period, Weighted-Average Exercise Price (in dollars per share)	$ 38.79
Exercised, Weighted-Average Exercise Price (in dollars per share)	28.89
Forfeited, Weighted-Average Exercise Price (in dollars per share)	37.11
Expired, Weighted-Average Grant Date Fair Value (in dollars per share)	58.78
Outstanding at the end of the period, Weighted-Average Exercise Price (in dollars per share)	39.88	$ 38.79
Exercisable balance at the end of the period, Weighted-Average Exercise Price (in dollars per share)	$ 40.94
Selected amounts pertaining to stock option exercises:
Issuances of common stock under employee stock plans	$ 18.0	$ 12.0	$ 1.0
Actual tax benefit realized from stock option exercises	3.0	2.0	1.0
Pre-tax intrinsic value of stock options exercised	12.0	$ 10.0	$ 2.0
Stock-based compensation costs
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 1.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	2 months 12 days
Restricted Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	36,567	37,870
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 41.84	$ 40.40
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	36,567
Selected amounts pertaining to stock option exercises:
Vesting period	3 years
Restricted stock activity, weighted-average exercise price
Granted, Weighted-Average Grant Date Fair Value (in dollars per share)	$ 41.84	$ 40.40	$ 27.31
Stock-based compensation costs
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 14.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 7 months 6 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(37,870)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 40.40
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	0
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 0
Restricted Stock \| Non-management member of Board of Directors
Selected amounts pertaining to stock option exercises:
Vesting period	1 year
Restricted Stock Units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	693,960	569,807
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 40.14	$ 38.79
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	356,110
Restricted stock activity, weighted-average exercise price
Granted, Weighted-Average Grant Date Fair Value (in dollars per share)	$ 41.94	$ 43.09	31.20
Stock-based compensation costs
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(196,611)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 40.26
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(35,346)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 41.04
Performance Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number	304,834	197,937
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value	$ 44.42	$ 43.64
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period	179,876
Restricted stock activity, weighted-average exercise price
Granted, Weighted-Average Grant Date Fair Value (in dollars per share)	$ 43.09	$ 44.59	$ 45.37
Stock-based compensation costs
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount	$ 9.0
Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition	1 year 8 months 12 days
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period	(59,407)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value	$ 40.62
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period	(13,572)
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value	$ 44.31

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Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

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Amount of cost not yet recognized for nonvested award under share-based payment arrangement.

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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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Amount of tax benefit for recognition of expense of award under share-based payment arrangement.

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Amount of tax benefit from exercise of option under share-based payment arrangement.

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Amount of cash inflow from exercise of option under share-based payment arrangement.

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

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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.

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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).

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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).

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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.

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Per share or unit weighted-average fair value of nonvested award under share-based payment arrangement. Excludes share and unit options.

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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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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.

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

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Rate of weighted-average expected volatility for award under share-based payment arrangement.

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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 highest quantity of shares an employee can purchase under the plan per period.

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Number of shares authorized for issuance under share-based payment arrangement.

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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.

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The number of shares into which fully or partially vested stock options outstanding as of the balance sheet date can be currently converted under the option plan.

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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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Amount by which the current fair value of the underlying stock exceeds the exercise price of options outstanding.

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Number of options outstanding, including both vested and non-vested options.

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Weighted average price at which grantees can acquire the shares reserved for issuance under the stock option plan.

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Weighted average price at which option holders acquired shares when converting their stock options into shares.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options of the plan that expired.

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Weighted average price at which grantees could have acquired the underlying shares with respect to stock options that were terminated.

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Expected term of 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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Amount of difference between fair value of the underlying shares reserved for issuance and exercise price of vested portions of options outstanding and currently exercisable.

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Weighted average remaining contractual term of exercisable stock options, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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Number of share options (or share units) exercised during the current period.

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