Common Stockholders' Equity (Schedule of Changes in Shares of Common Stock Outstanding) (Details)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Common Stock Shares Outstanding [Roll Forward]
Balance, beginning of year	136,017,732	137,520,019	141,009,834
Shares issued	139,790	2,114,168	2,702,303
Shares repurchased	(3,924,355)	(3,616,455)	(6,192,118)
Balance, end of year	132,233,167	136,017,732	137,520,019