Retirement Benefits (Details 8) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	$ (1.0)	$ (2.3)
Net actuarial loss	(1,425.1)	(1,460.4)
Accumulated other comprehensive loss	(1,426.1)	(1,462.7)	$ (1,418.2)
Deferred tax effect	525.6	543.4
Accumulated other comprehensive loss, net of tax	(900.5)	(919.3)
Other Postretirement Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	11.7	14.6
Net actuarial loss	(95.4)	(89.0)
Accumulated other comprehensive loss	(83.7)	(74.4)	$ (101.4)
Deferred tax effect	29.7	28.2
Accumulated other comprehensive loss, net of tax	$ (54.0)	$ (46.2)