Retirement Benefits - Narrative - Plan Descriptions (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2016	Nov. 30, 2015	Nov. 30, 2014
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan assets, total	$ 931.4	$ 925.1
Unfunded pension obligation	580.6	548.2
Expected cash contributions		$ 72.0
First 3% of Compensation Contributed
Defined Benefit Plan Disclosure [Line Items]
Percent of company matching compensation contributed		100.00%
Percent of participant's compensation contributed		3.00%
Cost of 401(k) plan	1.3	$ 20.7	$ 24.9	$ 24.4
Defined Contribution 401(k) Plan, Next Three Percent Contributed
Defined Benefit Plan Disclosure [Line Items]
Percent of company matching compensation contributed		50.00%
Percent of participant's compensation contributed		3.00%
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan assets, total	931.4	$ 925.1	964.1
Projected benefit obligations, total	1,531.0	1,492.1	$ 1,549.5
Unfunded pension obligation	580.6	548.2
Employer contributions	$ 0.1	34.1
Contributions by employer, recoverable in current year government contracts		27.5
Defined Benefit Plan, Contributions by Employer, Recoverable in Future Fiscal Years		5.3
Qualified Plan | Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Employer contributions		$ 32.8