Stock-based Compensation (Details 2) (Performance Shares [Member], USD $) In Millions, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013	Dec. 31, 2012
Performance Shares [Member]
Schedule of information on stock units
Undistributed, Beginning Balance	0.7
Undistributed, Weighted-Average Grant Date Fair Value per Share, Beginning Balance	$ 47.83
Granted	0.1
Granted, Weighted-Average Grant Date Fair Value per Share	$ 88.26		$ 78.00	$ 48.64
Additional shares earned	0.2
Additional shares earned, Weighted-Average Grant Date Fair Value per Share	$ 31.78
Distributed	(0.2)
Distributed, Weighted-Average Grant Date Fair Value per Share	$ 44.85
Forfeited	0
Forfeited, Weighted-Average Grant Date Fair Value per Share	$ 0.00
Undistributed, Ending Balance	0.8	[1]	0.7
Undistributed, Weighted-Average Grant Date Fair Value per Share, Ending Balance	$ 49.47	[1]	$ 47.83

[1] Undistributed performance share units include approximately 0.4 million units with a weighted-average grant date fair value of $68.27 per share that had not yet vested and 0.4 million units that have vested but were not yet distributed.