Employee Benefit Plans (Fair Values of Pension Plan Assets by Category) (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 318.6	$ 292.5
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.9	5.3
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	314.7	287.2
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.9	5.3
Cash and Cash Equivalents [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.9	5.3
Cash and Cash Equivalents [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Cash and Cash Equivalents [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. Equity [Member] | Commingled Pools / Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34.7	69.5
U.S. Equity [Member] | Commingled Pools / Collective Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
U.S. Equity [Member] | Commingled Pools / Collective Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	34.7	69.5
U.S. Equity [Member] | Commingled Pools / Collective Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Commingled Pools / Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.2	47.6
International Equity [Member] | Commingled Pools / Collective Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Commingled Pools / Collective Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.2	47.6
International Equity [Member] | Commingled Pools / Collective Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Trust for Benefit of Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.6	4.7
International Equity [Member] | Trust for Benefit of Employees [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Trust for Benefit of Employees [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	4.6	4.7
International Equity [Member] | Trust for Benefit of Employees [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Pension Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.3	13.5
International Equity [Member] | Pension Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
International Equity [Member] | Pension Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	3.3	13.5
International Equity [Member] | Pension Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Commingled Pools / Collective Trusts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	197.9	134.9
Fixed Income [Member] | Commingled Pools / Collective Trusts [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Commingled Pools / Collective Trusts [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	197.9	134.9
Fixed Income [Member] | Commingled Pools / Collective Trusts [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Trust for Benefit of Employees [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.6	11.9
Fixed Income [Member] | Trust for Benefit of Employees [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Trust for Benefit of Employees [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	13.6	11.9
Fixed Income [Member] | Trust for Benefit of Employees [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Pension Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.9	5.1
Fixed Income [Member] | Pension Fund [Member] | Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Fixed Income [Member] | Pension Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.9	5.1
Fixed Income [Member] | Pension Fund [Member] | Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	$ 0.0
Blend [Domain] | Pension Fund [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	12.5
Blend [Domain] | Pension Fund [Member] | Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 12.5