Retirement Benefits (Details 8) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Pension Benefits [Member]
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	$ (10.6)	$ (11.2)
Net actuarial loss	(1,589.7)	(1,558.5)
Accumulated other comprehensive loss	(1,600.3)	(1,569.7)	$ (1,470.3)
Deferred tax effect	561.4	555.7
Accumulated other comprehensive loss, net of tax	(1,038.9)	(1,014.0)
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Prior service (cost) credit	7.0	11.0
Net actuarial loss	(126.1)	(114.5)
Accumulated other comprehensive loss	(119.1)	(103.5)	$ (107.0)
Deferred tax effect	38.1	34.4
Accumulated other comprehensive loss, net of tax	$ (81.0)	$ (69.1)