Net Income Per Common Share (Schedule of Average Shares Excluded From Diluted Net Income Per Common Share Computation) (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock Options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Average outstanding securities	7.2	10.8	16.0
Stock Options | Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exercise price	47.24	34.78	29.81
Stock Options | Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exercise price	61.94	61.94	64.50
Warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Average outstanding securities	0	0	0.3
Warrants | Minimum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exercise price	0.00	0.00	30.36
Warrants | Maximum
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Exercise price			30.36