Retirement Plans - Reconciliation of Funded Status (Details) - USD ($)
$ in Millions |
12 Months Ended |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Pension Plan |
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
| Benefit obligation at beginning of year |
$ 3.2
|
$ 3,631.1
|
|
| Interest cost |
2.4
|
147.3
|
$ 161.7
|
| Actuarial gain |
(24.7)
|
(254.0)
|
|
| Plan transfer |
317.0
|
(3,363.2)
|
|
| Benefits paid |
(4.6)
|
(158.0)
|
|
| Benefit obligation at end of year |
293.3
|
3.2
|
3,631.1
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
| Fair value of plan assets at beginning of year |
0.0
|
3,219.9
|
|
| Actual return on assets |
(9.6)
|
(33.8)
|
|
| Employer contributions |
1.3
|
0.0
|
|
| Plan transfer |
248.7
|
(3,028.1)
|
|
| Benefits paid |
(4.6)
|
(158.0)
|
|
| Fair value of plan assets at end of year |
235.8
|
0.0
|
$ 3,219.9
|
| Funded status at end of year |
(57.5)
|
(3.2)
|
|
| Other Postretirement Benefit Plan |
|
|
|
| Defined Benefit Plan, Change in Benefit Obligation [Roll Forward] |
|
|
|
| Benefit obligation at beginning of year |
0.0
|
|
|
| Interest cost |
0.0
|
|
|
| Actuarial gain |
(0.3)
|
|
|
| Plan transfer |
1.5
|
|
|
| Benefits paid |
0.0
|
|
|
| Benefit obligation at end of year |
1.2
|
0.0
|
|
| Defined Benefit Plan, Change in Fair Value of Plan Assets [Roll Forward] |
|
|
|
| Fair value of plan assets at beginning of year |
0.0
|
|
|
| Actual return on assets |
0.0
|
|
|
| Employer contributions |
0.0
|
|
|
| Plan transfer |
0.0
|
|
|
| Benefits paid |
0.0
|
|
|
| Fair value of plan assets at end of year |
0.0
|
$ 0.0
|
|
| Funded status at end of year |
$ (1.2)
|
|
|