Common Stockholders' Equity (Schedule of Changes in Shares of Common Stock Outstanding) (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Common Stock Shares Outstanding [Roll Forward]
Balance, beginning of year	141,010	156,552	161,467
Shares issued	2,702	2,272	1,467
Shares repurchased	(6,192)	(17,814)	(6,382)
Balance, end of year	137,520	141,010	156,552