Pension and Other Postretirement Benefit Plans (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Components of Net Periodic Benefit Cost (Income) [Abstract]
Employer Contributions to Defined Benefit Pension Plans - Common Stock Value			$ 13.5	$ 0.0
Pension [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service Cost	$ 2.6	$ 2.0	7.7	6.1
Interest Cost	8.1	8.2	24.4	24.4
Expected Return on Plan Assets	(10.6)	(10.7)	(31.8)	(32.0)
Amortization of Prior Service Credits	0.0	0.0	0.0	0.0
Amortization of Net Loss	2.5	2.4	7.4	7.3
Net Periodic Benefit Cost (Income)	2.6	1.9	7.7	5.8
Employer Contributions to Defined Benefit Pension Plans - Common Stock Value			13.5
Employer Contributions to Defined Benefit Plans			1.7	6.3
Expected Future Employer Contributions in 2017	0.0		0.0
Other Postretirement [Member]
Components of Net Periodic Benefit Cost (Income) [Abstract]
Service Cost	1.1	1.0	3.3	3.0
Interest Cost	2.0	1.9	5.8	5.6
Expected Return on Plan Assets	(2.6)	(2.8)	(7.9)	(8.4)
Amortization of Prior Service Credits	(0.5)	(0.7)	(1.5)	(2.2)
Amortization of Net Loss	0.0	0.0	0.2	0.1
Net Periodic Benefit Cost (Income)	0.0	$ (0.6)	(0.1)	(1.9)
Employer Contributions to Defined Benefit Plans			0.0	$ 0.0
Expected Future Employer Contributions in 2017	$ 0.0		$ 0.0