Retirement Benefits - Schedule of Components of Retirement Benefit Expense (Income) (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Dec. 31, 2015	Mar. 31, 2016	Feb. 28, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.1	$ 3.5	$ 2.7
Interest cost on benefit obligation	5.3	16.0	15.9
Assumed return on plan assets	(6.0)	(17.5)	(22.0)
Amortization of prior service credits	0.0	0.0	0.0
Recognized net actuarial losses (gains)	5.4	15.9	20.9
Retirement benefit expense (benefit)	5.8	17.9	17.5
Postretirement Medical and Life Insurance Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0
Interest cost on benefit obligation	0.2	0.5	0.5
Assumed return on plan assets	0.0	0.0	0.0
Amortization of prior service credits	(0.1)	(0.3)	(0.3)
Recognized net actuarial losses (gains)	(0.3)	(0.9)	(0.9)
Retirement benefit expense (benefit)	$ (0.2)	$ (0.7)	$ (0.7)