Capital Stock (Narrative) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2012 2012 $405.0 Million Repurchase Agreement [Member]	Sep. 30, 2013 2011 $500.0 Million Repurchase Agreement [Member]	Dec. 31, 2011 2011 $500.0 Million Repurchase Agreement [Member]	Sep. 30, 2013 2010 $500.0 Million Repurchase Agreement [Member]	Dec. 31, 2010 2010 $500.0 Million Repurchase Agreement [Member]
Stock Repurchase Program, Authorized Amount		$ 405		$ 500		$ 500
Stock Repurchased and Retired During Period, Shares	3.9		2.5		1.4
Stock Repurchased and Retired During Period, Value	252		157		95
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 748		$ 343