Earnings Per Share (Details) In Millions, unless otherwise specified	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Earnings Per Share [Abstract]
Weighted-average basic common shares outstanding (in shares)	175.5	175.4	175.4	177.0	175.5	177.2
Potential number of shares issuable under the Company's LTSIP (in shares)	0	1.1	0.7	1.1	0.6	1.1
Weighted-average diluted common shares outstanding (in shares)	175.5	176.5	176.1	178.1	176.1	178.3