Retirement Benefits - Summary of Components of Retirement Benefit Expense (Income) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Nov. 30, 2015	Nov. 30, 2014
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 1.1	$ 14.0	$ 10.8	$ 8.8
Interest cost on benefit obligation	5.3	64.1	63.6	67.1
Assumed return on plan assets	(6.0)	(70.1)	(88.1)	(92.6)
Amortization of prior service costs (credits)	0.0	0.1	0.0	0.0
Amortization of net losses (gains)	5.4	63.7	84.0	54.4
Retirement benefit expense (income)	5.8	71.8	70.3	37.7
Medical and Life Insurance Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	0.0	0.0	0.0	0.1
Interest cost on benefit obligation	0.2	1.9	1.9	2.5
Assumed return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service costs (credits)	(0.1)	(1.2)	(1.1)	(0.9)
Amortization of net losses (gains)	(0.3)	(3.6)	(3.5)	(2.9)
Retirement benefit expense (income)	$ (0.2)	$ (2.9)	$ (2.7)	$ (1.2)