Represents the number of variable interest payment obligations that are settled periodically by swap contracts.

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- Definition

Represents the time period of historical volatility of stock used to estimate expected volatility, in years.

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The percentage estimated forfeiture rate based on historical experience at the date of the grant.

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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- Definition

The reference rate for the variable rate of the interest rate derivative, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

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- Definition

As of the balance sheet date, the aggregate unrecognized cost of equity-based awards made to employees under equity-based compensation awards that have yet to vest.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Subparagraph h
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- Definition

Aggregate notional amount of all interest rate derivatives designated as hedging instruments in cash flow hedges. Notional amount refers to the monetary amount specified in the interest rate derivative contract.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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- Definition

Description of the period of time over which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, which may be expressed in a variety of ways (for example, in years, month and year).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
-Number 123R
-Paragraph A240
-Subparagraph a
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-Name Accounting Standards Codification
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-Paragraph 2
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- Definition

The period of time an equity-based award is expected to be outstanding. An equity-based award's expected term is generally determined based on, among other factors, the instrument's contractual term and the effects of employees' expected exercise and post-vesting employment termination behavior.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Paragraph 2
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- Definition

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.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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- Definition

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

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Statement of Financial Accounting Standard (FAS)
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-Subparagraph e(2)(d)
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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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Summary of Significant Accounting Policies (Details 3) (USD $) In Millions, unless otherwise specified	6 Months Ended		3 Months Ended		6 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011 Phantom stock unit awards	Dec. 31, 2010 Phantom stock unit awards	Jun. 30, 2011 Phantom stock unit awards	Jun. 30, 2011 Stock appreciation rights	Mar. 31, 2011 Stock appreciation rights	Jun. 30, 2011 Stock appreciation rights
Stock-Based Compensation
Time period of historical volatility of stock used to estimate expected volatility (in years)	5.77
Weighted-average assumptions used in the Black-Scholes option-pricing model
Risk-free interest rate (as a percent)	2.04%	2.00%
Expected volatility (as a percent)	47.24%	49.18%
Weighted-average expected life (in years)	5.77	5.68
Forfeiture rate (as a percent)	5.00%	5.00%
Share based compensation arrangement by share based payment award
Vesting period (in years)				Five years			Four years
Unrecognized compensation cost			$ 7.6		$ 7.6	$ 5.6		$ 5.6
Recognized compensation expense			0.6		1.0	0.4		0.7
Summary of derivative instruments
Number of variable interest payment obligations	2
Notional value of cash flow hedges	$ 540
Reference rate of swap yield curve used to determine fair value of interest rate swaps	LIBOR