STOCK-BASED COMPENSATION - PERFORMANCE STOCK RIGHTS (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Performance Stock Rights
Assumptions incorporated into the valuation models
Risk-free interest rate, minimum (as a percent)	0.21%	0.13%	0.17%
Risk-free interest rate, maximum (as a percent)	0.63%	1.27%	1.27%
Expected volatility, minimum (as a percent)	18.00%	15.00%	14.00%
Expected volatility, maximum (as a percent)	22.00%	36.00%	36.00%
Additional disclosures
Compensation cost not yet recognized	$ 4.2
Weighted-average period over which compensation cost is to be recognized	1 year 7 months
Total intrinsic value of performance stock rights distributed during the period	6.4	8.8	4.7
Tax benefit realized from the distribution of shares	$ 2.6	$ 3.6	$ 1.9
Performance Stock Rights \| Minimum
Assumptions incorporated into the valuation models
Expected dividend yield (as a percent)	5.25%	5.28%	5.18%
Performance Stock Rights \| Maximum
Assumptions incorporated into the valuation models
Expected dividend yield (as a percent)	5.33%	5.34%	5.34%
Performance Stock Rights Accounted For As Equity Awards
Performance Stock Rights
Outstanding at the beginning of the period (in shares)	85,749
Granted (in shares)	21,146
Award modifications (in shares)	64,612
Distributed (in shares)	(74,345)
Adjustment for estimated payout and shares not distributed (in shares)	(28,591)
Forfeited (in shares)	(308)
Outstanding at the end of the period (in shares)	68,263	85,749
Weighted-Average Fair Value
Outstanding at the beginning of the period (in dollars per share)	$ 46.62
Granted (in dollars per share)	$ 44.28	$ 48.50	$ 52.70
Award modifications (in dollars per share)	$ 85.09
Distributed (in dollars per share)	$ 77.67
Adjustment for estimated payout and shares not distributed (in dollars per shares)	$ 52.67
Forfeited (in dollars per share)	$ 44.28
Outstanding at the end of the period (in dollars per share)	$ 58.54	$ 46.62
Performance Stock Rights Accounted For As Equity Awards \| Performance stock rights with a performance period ending December 31, 2013
Performance Stock Rights
Distributed (in shares)	0
Performance Stock Rights Accounted For As Liability Awards
Performance Stock Rights
Outstanding at the beginning of the period (in shares)	198,904
Granted (in shares)	84,529
Award modifications (in shares)	(64,612)
Distributed (in shares)	(10,760)
Adjustment for estimated payout and shares not distributed (in shares)	(36,519)
Forfeited (in shares)	(1,234)
Outstanding at the end of the period (in shares)	170,308
Weighted-Average Fair Value
Outstanding at end of the period, fair value as of the reporting date (in dollars per share)	$ 108.51
Performance Stock Rights Accounted For As Liability Awards \| Performance stock rights with a performance period ending December 31, 2013
Performance Stock Rights
Distributed (in shares)	0

Represents the aggregate tax benefit realized from the distribution of shares during the reporting period.

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Adjustment to total shares outstanding to reflect the difference between the number of shares included in the beginning balance and the number of shares paid out during the period on other than stock (or unit) option plans.

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Weighted-average fair value as of the grant date of equity-based awards other than stock (unit) options for which an adjustment was made to the total shares outstanding to reflect the difference between the number of shares included in the beginning balance and the number of shares paid out during the period.

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Represents the number of equity-based payment instruments modified during the period on other than stock (or unit) option plans.

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The weighted-average fair value as of the grant date of equity-based awards that were modified during the period on other than stock (or unit) option plans.

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Represents the number of shares distributed during the period on other than stock (or unit) option plans.

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Represents the total intrinsic value of equity-based instruments, excluding stock (or unit) options, distributed during the reporting period.

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Weighted-average fair value as of the grant date of equity-based awards other than stock (unit) options that were distributed during the period as per the agreement made under the plan.

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The weighted average fair value as of the reporting date 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.

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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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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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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.

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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 estimated measure of the maximum 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 estimated measure of the minimum 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 maximum risk-free interest rate assumption that is used in valuing an option on its own shares.

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

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