Common Stockholders' Equity (Schedule of Changes in Shares of Common Stock Outstanding) (Details) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Common Stock Shares Outstanding [Roll Forward]
Balance, beginning of year	137,520	141,010	156,552
Shares issued	2,114	2,702	2,272
Shares repurchased	(3,616)	(6,192)	(17,815)
Balance, end of year	136,018	137,520	141,010