Retirement Benefits - Schedule of Net Benefit Costs (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended				12 Months Ended
	Sep. 30, 2014		Sep. 30, 2013		Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Compensation and Retirement Disclosure [Abstract]
Service cost	$ 1.1		$ 1.3		$ 1.7	$ 1.5	$ 1.3
Interest cost	1.9		1.5		2.0	2.2	2.2
Expected return on plan assets	(2.1)		(1.8)		(2.4)	(2.1)	(2.2)
Amortization of actuarial losses	0.3	[1]	0.8	[1]	1.0	0.9	0.4
Net periodic benefit cost	$ 1.2		$ 1.8		$ 2.3	$ 2.5	$ 1.7

[1] Reflects amounts reclassified from accumulated other comprehensive income (loss) to net income.