Share Based Compensation (Tables)

12 Months Ended

Dec. 31, 2013

Disclosure of Compensation Related Costs, Share-based Payments [Abstract]

Stock Options Valuation Assumptions

We estimated the fair value of each stock option granted on the date of grant using a Black-Scholes option valuation model that uses the assumptions noted in the following table. We based expected volatility on a 50% weighting of our historical volatilities and 50% weighting of implied USG volatilities. The risk-free rate was based on zero-coupon U.S. government issues at the time of grant. The expected term was developed using the simplified method, as permitted by the Securities and Exchange Commission because there is not sufficient historical stock option exercise experience available.

Assumptions:	2012		2011
Expected volatility	59.03	%	55.88	%
Risk-free rate	1.24	%	2.85	%
Expected term (in years)	6.26		6.25
Expected dividends	—		—

Stock Options Activity

A summary of stock options outstanding as of December 31, 2013 and of stock option activity during the fiscal year then ended is presented below:

	Number of Options (000)		Weighted Average Exercise Price		Weighted Average Remaining Contractual Term (years)	Aggregate Intrinsic Value (millions)
Outstanding at January 1, 2013	5,063		$	25.02	6.18	$	45
Exercised	(377	)	10.34
Canceled	(197	)	41.28
Forfeited	—		—
Outstanding at December 31, 2013	4,489		$	25.54	5.21	$	39
Exercisable at December 31, 2013	3,602		$	27.98	5.51	$	28
Vested or expected to vest at December 31, 2013	4,482		$	25.55	5.20	$	39

Nonvested Restricted Stock Units Activity

RSUs outstanding as of December 31, 2013 and RSU activity during 2013 were as follows:

	Number of Shares (000)		Weighted Average Grant Date Fair Value
Nonvested at January 1, 2013	1,249		$	14.74
Granted	40		29.44
Vested	(487	)	13.54
Forfeited	(2	)	30.31
Nonvested at December 31, 2013	800		16.15

Performance Based Units Valuation Assumptions

We estimated the fair value of each performance share granted on the date of grant using a Monte Carlo simulation that uses the assumptions noted in the following table. Expected volatility is based on implied volatility of our traded options and the daily historical volatilities of our peer group. The risk-free rate was based on zero coupon U.S. government issues at the time of grant. The expected term represents the period from the grant date to the end of the three-year performance period.

Assumptions:	2013		2012		2011
Expected volatility	59.98	%	67.63	%	77.84	%
Risk-free rate	0.43	%	0.36	%	1.20	%
Expected term (in years)	2.88		2.89		2.89
Expected dividends	—		—		—

Nonvested Performance-based Units Activity

Nonvested performance shares outstanding as of December 31, 2013 and performance share activity during 2013 were as follows:

	Weighted Number of Shares (000)		Weighted Average Grant Date Fair Value
Nonvested at January 1, 2013	360		$	25.29
Granted	105		38.89
Vested	(152	)	28.40
Forfeited	(5	)	26.10
Nonvested at December 31, 2013	308		28.36