Earnings Per Share (Details) - shares shares in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Earnings Per Share [Abstract]
Weighted-average basic common shares outstanding (in shares)	176.2	175.8	176.3	175.8	176.2	175.7
Potential number of shares issuable under the Company's LTSIP (in shares)	0.1	0.3	0.2	0.3	0.2	0.3
Weighted-average diluted common shares outstanding (in shares)	176.3	176.1	176.5	176.1	176.4	176.0