Retirement Benefits Fair Value Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Defined Benefit Plan Disclosure [Line Items]
Employer stock included in plan assets	$ 40.0	$ 34.7
Pension Plan
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	705.1	757.6	$ 835.7
Pension Plan | Fair Value, Measurements, Recurring
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	705.1	757.6
Investments Priced Using Net Asset Value	86.5	92.4
Pension Plan | Fair Value, Measurements, Recurring | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48.3	62.0
Pension Plan | Fair Value, Measurements, Recurring | US Large-Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29.5	29.0
Pension Plan | Fair Value, Measurements, Recurring | US Mid-Cap and Small-Cap Growth
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.6	38.2
Pension Plan | Fair Value, Measurements, Recurring | International Large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27.6	28.7
Pension Plan | Fair Value, Measurements, Recurring | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.9	11.8
Pension Plan | Fair Value, Measurements, Recurring | US Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	334.5	186.4
Pension Plan | Fair Value, Measurements, Recurring | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	21.0	99.6
Pension Plan | Fair Value, Measurements, Recurring | Asset Backed Securities and Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.0	126.6
Pension Plan | Fair Value, Measurements, Recurring | Equity/Debt Futures
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	2.1	2.5
Pension Plan | Fair Value, Measurements, Recurring | Derivative Liability
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(1.1)	(0.7)
Pension Plan | Fair Value, Measurements, Recurring | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	133.5	158.3
Investments Priced Using Net Asset Value	86.5	92.4
Pension Plan | Fair Value, Measurements, Recurring | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	16.2	15.2
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	202.0	237.6
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	48.3	62.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | US Large-Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	29.5	29.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | US Mid-Cap and Small-Cap Growth
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	42.6	38.2
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | International Large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	27.6	28.7
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	5.9	11.8
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | US Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.3	0.3
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Asset Backed Securities and Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity/Debt Futures
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.5	1.6
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivative Liability
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.5)	(0.7)
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	47.0	65.9
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.8	0.8
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	416.5	427.2
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | US Large-Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | US Mid-Cap and Small-Cap Growth
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | International Large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | US Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	334.5	186.4
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	20.6	98.9
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Asset Backed Securities and Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	45.0	126.6
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Equity/Debt Futures
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	1.6	0.9
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Derivative Liability
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	(0.6)	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Similar Assets (Level 2) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	15.4	14.4
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | US Large-Cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | US Mid-Cap and Small-Cap Growth
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | International Large-cap
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Emerging Markets
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | US Treasuries
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Corporate Bonds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.1	0.4
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Asset Backed Securities and Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Equity/Debt Futures
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Derivative Liability
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Alternative Investment Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	0.0	0.0
Pension Plan | Fair Value, Measurements, Recurring | Unobservable inputs for which little or no market data exists (Level 3) | Common Pooled Fund
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	$ 0.0	$ 0.0