Pension and Other Postretirement Benefits (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Net periodic pension and OPEB costs:
Service cost - benefits earned during the year	$ 2.3	$ 2.8	$ 7.3	$ 8.9
Interest cost on projected benefit obligation	32.5	35.5	99.9	107.8
Expected return on plan assets	(38.0)	(44.0)	(118.0)	(132.7)
Amortization of prior service cost (benefit)	0.3	(0.2)	0.6	0.0
Amortization of net actuarial loss (gain)	7.4	12.1	23.0	35.2
Curtailment (gain) loss			0.0	(1.0)
Defined Benefit Plan Expected Participant Contributions	(0.1)	(0.2)	(0.4)	(0.6)
Net periodic pension and OPEB cost	4.4	6.0	12.4	17.6
Contributions paid to defined benefit plans			10.0
Defined Benefit Plan, Expected Contributions in Current Fiscal Year			12.0
Defined Benefit Plans
Net periodic pension and OPEB costs:
Service cost - benefits earned during the year	1.9	2.1	5.7	7.3
Interest cost on projected benefit obligation	31.0	33.9	95.5	103.2
Expected return on plan assets	(38.0)	(44.0)	(118.0)	(132.7)
Amortization of prior service cost (benefit)	0.2	0.2	0.6	0.6
Amortization of net actuarial loss (gain)	7.4	12.1	23.0	35.2
Curtailment (gain) loss			0.0	(1.0)
Defined Benefit Plan Expected Participant Contributions	(0.1)	(0.2)	(0.4)	(0.6)
Net periodic pension and OPEB cost	2.4	4.1	6.4	12.0
Other Postretirement Benefits
Net periodic pension and OPEB costs:
Service cost - benefits earned during the year	0.4	0.7	1.6	1.6
Interest cost on projected benefit obligation	1.5	1.6	4.4	4.6
Expected return on plan assets	0.0	0.0	0.0	0.0
Amortization of prior service cost (benefit)	0.1	(0.4)	0.0	(0.6)
Amortization of net actuarial loss (gain)	0.0	0.0	0.0	0.0
Curtailment (gain) loss			0.0	0.0
Defined Benefit Plan Expected Participant Contributions	0.0	0.0	0.0	0.0
Net periodic pension and OPEB cost	$ 2.0	$ 1.9	$ 6.0	$ 5.6