Summary of Significant Accounting Policies Earnings Per Share (Details) - shares shares in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Earnings Per Share, Diluted, by Common Class, Including Two Class Method [Line Items]
Antidilutive shares excluded from computation of EPS		0.3
Used in basic calculation	176.6	179.8	179.2
Potential number of shares issuable upon excerise of in-the-money stock options under the Long-term Stock Incentive Plan	0.0	0.0	0.3
Average diluted common shares outstanding (in shares)	176.6	179.8	179.5