Stock-Based Compensation Plans (Tables)

12 Months Ended

Dec. 31, 2011

Stock-Based Compensation Plans [Abstract]

Total compensation expense for all stock-based compensation plans

Stock-based compensation expense recognized was as follows:

	Year Ended December 31,
(dollars in millions)	2011		2010		2009
Outstanding restricted and deferred stock unit and award grants	$	25.6	$	26.0	$	18.5
Unvested outstanding stock option grants		11.1		8.5		9.2
Total stock-based compensation expense	$	36.7	$	34.5	$	27.7

Summary of activity in all stock based compensation plans

A summary of option activity under the Company's stock compensation plans as of and for the year ended December 31, 2011 is presented below: 

Options	Shares			Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (in years)		Aggregate Intrinsic Value (dollars in millions)
Outstanding at January 1, 2011		6,253,118		$	34.72		5.30	$	100.1
Granted		725,071			51.24
Exercised		(1,176,125	)		27.48
Forfeited		(24,108	)		39.80
Expired		(20,500	)		11.57
Outstanding at December 31, 2011		5,757,456		$	38.36		4.55	$	63.8
Vested at December 31, 2011 or expected to vest in the future		5,735,564		$	38.33		4.53	$	63.8
Exercisable at December 31, 2011		3,813,517		$	34.78		3.22	$	54.9

The fair values per share of option grants for the years ended December 31, 2011, 2010 and 2009 were estimated using the Black-Scholes-Merton option pricing formula with the following weighted-average assumptions: 

	Year Ended December 31,
	2011			2010			2009
Expected life (in years)		2.8			2.5			2.4
Risk-free interest rate		0.38	%		0.46	%		1.1	%
Volatility		42.6	%		43.8	%		32.0	%
Expected dividend yield		0.0	%		0.0	%		0.0	%

    The Company determined the assumptions involving the expected life of its options and volatility rates based primarily on historical data and consideration of expectations for the future.

The above assumptions and market prices of the Company's common stock at the date of option exercises resulted in the following values:

	Year Ended December 31,
	2011			2010		2009
Grant-date fair value per option	$	14.47	$	11.78	$	8.10
Intrinsic value of options exercised (dollars in millions)	$	31.5	$	63.4	$	23.5
Average intrinsic value per share of options exercised	$	26.79	$	22.46	$	19.26

A summary of restricted and deferred stock unit award activity under the Company's stock compensation plans as of and for the year ended December 31, 2011 is presented below: 

Restricted and Deferred Stock Units	Number			Weighted-Average Grant Date Fair Value
Nonvested at January 1, 2011		1,941,399		$	35.02
Granted		682,246			50.67
Vested		(661,146	)		50.89
Forfeited		(53,144	)		38.99
Nonvested at December 31, 2011		1,909,355		$	30.25

Total unrecognized compensation expense for all stock-based compensation plans

	At
	December 31, 2011
Stock-based compensation cost not yet recognized under the straight-line method (dollars in millions)	$	18.1
Weighted-average remaining expense recognition period (in years)		1.85

	At December 31, 2011
Stock-based compensation cost not yet recognized under the straight-line method (dollars in millions)	$	34.7
Weighted-average remaining expense recognition period (in years)		1.56

Restricted and deferred stock units granted and vesting

Information on restricted and deferred stock units granted and vesting during the three years ended December 31, 2011 follows:

	Year Ended December 31,
	2011		2010		2009
Number of units granted with performance conditions		139,191		211,804		–
Intrinsic value of units vesting (dollars in millions)	$	36.9	$	29.2	$	11.0
Total number of units granted		682,246		806,041		616,904
Weighted average grant date fair value per unit	$	50.67	$	41.81	$	25.44