Common Stock (Tables)

12 Months Ended

Dec. 31, 2011

Common Stock [Abstract]

Assumptions used for calculating the fair values of stock option awards

	Year Ended December 31,
	2011			2010			2009
Stock Options Granted
Weighted average grant date fair value, per share	$	26.13		$	11.76		$	1.34
Weighted average assumptions used:
Expected volatility		70.1	%		75.4	%		82.6	%
Expected lives		4.8			4.6			4.5
Risk-free interest rates		1.8	%		2.2	%		1.48	%
Dividends yields		0.00	%		0.00	%		0.00	%

Stock options status and activity

	Year Ended December 31, 2011
	Shares Under Option			Weighted  Avg. Exercise Prices		Weighted  Avg. Remaining Life in Years		Aggregate Intrinsic Value
	(Millions)
Outstanding Stock Options
Outstanding, January 1, 2011		3,168,474		$	14.27		4.3	$	68
Granted		201,133			45.42
Expired		(56,046	)		3.66
Forfeited		(13,184	)		9.36
Exercised		(125,624	)		17.10				3
Outstanding, March 31, 2011		3,174,753		$	16.34		4.4	$	80
Granted		2,711			43.51
Forfeited		(23,841	)		14.26
Exercised		(82,166	)		11.50				3
Outstanding, June 30, 2011		3,071,457		$	16.51		4.2	$	76
Granted		1,649			44.02
Forfeited		(450	)		4.03
Exercised		(115,249	)		8.94				3
Outstanding, September 30, 2011		2,957,407		$	16.83		4.0	$	54
Granted		173			24.97
Expired		(10,000	)		1.57
Forfeited		(17,716	)		1.82
Exercised		(186,665	)		10.19				3
Outstanding, December 31, 2011		2,743,199		$	17.43		4.0	$	37
Vested and Expected to Vest, December 31, 2011		2,700,577			17.17		4.0	$	37
Exercisable, December 31, 2011		2,164,226		$	15.95		3.9	$	30

Nonvested restricted shares

	Year Ended December 31, 2011
	Shares			Weighted Avg. Grant Date Fair Value
Nonvested Restricted Shares
Nonvested balance at January 1, 2011		558,198		$	11.58
Granted		141,036			45.42
Vested		(268,891	)		12.00
Forfeited		(4,822	)		13.74
Nonvested balance at March 31, 2011		425,521		$	22.51
Granted		1,381			43.51
Vested		(3,851	)		15.47
Forfeited		(7,190	)		23.82
Nonvested balance at June 30, 2011		415,861		$	22.62
Granted		1,042			44.02
Vested		(3,206	)		15.41
Forfeited		(158	)		1.86
Nonvested balance at September 30, 2011		413,539		$	22.74
Granted		109			24.97
Vested		(5,735	)		29.92
Forfeited		(162	)		1.87
Nonvested balance at December 31, 2011		407,751		$	22.64