Retirement Benefits (Details 7) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Amortization of net actuarial loss	$ 89.5	$ 85.3	$ 87.2
Amortization to net income (loss) of net prior service credits	(1.8)	(3.1)	(2.6)
Settlement gain	21.9	0.0	0.0
Net gain (loss) arising during the period	155.9	(128.4)	(180.5)
Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(1,600.3)	(1,569.7)
Amortization of net actuarial loss	75.6	74.5
Amortization to net income (loss) of net prior service credits	0.6	0.7
Settlement gain	0.0	0.0
Net gain (loss) arising during the period	147.6	(105.8)
End of year accumulated other comprehensive loss	(1,376.5)	(1,600.3)	(1,569.7)
Net change in accumulated other comprehensive loss	223.8	(30.6)
Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss), before Tax [Roll Forward]
Beginning of year accumulated other comprehensive loss	(119.1)	(103.5)
Amortization of net actuarial loss	13.9	10.8
Amortization to net income (loss) of net prior service credits	(2.4)	(3.8)
Settlement gain	(21.9)	0.0
Net gain (loss) arising during the period	8.3	(22.6)
End of year accumulated other comprehensive loss	(121.2)	(119.1)	$ (103.5)
Net change in accumulated other comprehensive loss	$ (2.1)	$ (15.6)