Pension and Other Retiree Benefits (Fair Value of Plan Assets) (Details) - Pension - USD ($) $ in Millions		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
U.S.
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 162.1	$ 150.5	$ 145.8
U.S. | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		151.4	102.8
U.S. | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1.7	38.2
U.S. | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
U.S. | Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			89.3
U.S. | Mutual Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		94.8	89.3
U.S. | Mutual Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Mutual Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		94.8
U.S. | Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0
U.S. | Equity Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0
U.S. | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		56.6	13.5
U.S. | Exchange traded funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		56.6	13.5
U.S. | Exchange traded funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
U.S. | Exchange traded funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
U.S. | Common collective trust funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1.7	7.9
U.S. | Common collective trust funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
U.S. | Common collective trust funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1.7	7.9
U.S. | Common collective trust funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
U.S. | Corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			16.3
U.S. | Corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Corporate debt securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			16.3
U.S. | Corporate debt securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Asset-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			3.4
U.S. | Asset-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Asset-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			3.4
U.S. | Asset-backed securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Multi-strategy hedge funds
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	[1]	9.0	9.5
U.S. | Government mortgage-backed securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			5.4
U.S. | Government mortgage-backed securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Government mortgage-backed securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			5.4
U.S. | Government mortgage-backed securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Collateralized mortgage obligations, mortgage backed securities, and other
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			5.2
U.S. | Collateralized mortgage obligations, mortgage backed securities, and other | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
U.S. | Collateralized mortgage obligations, mortgage backed securities, and other | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			5.2
U.S. | Collateralized mortgage obligations, mortgage backed securities, and other | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets			0.0
International
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		463.8	302.7	$ 318.9
International | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		121.1	99.7
International | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		291.0	193.4
International | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Cash and cash equivalents
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2.2	0.5
International | Cash and cash equivalents | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		2.2	0.5
International | Cash and cash equivalents | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Cash and cash equivalents | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		102.0	99.2
International | Equity Funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		102.0	99.2
International | Equity Funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Equity Funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Exchange traded funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		16.9
International | Exchange traded funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		16.9
International | Exchange traded funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0
International | Exchange traded funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0
International | Foreign corporate debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		72.2	145.3
International | Foreign corporate debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Foreign corporate debt securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		72.2	145.3
International | Foreign corporate debt securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Multi-strategy hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		133.4	20.2
Investments Net Asset Value	[1]	30.5
International | Multi-strategy hedge funds | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Multi-strategy hedge funds | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		133.4	20.2
International | Multi-strategy hedge funds | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Insurance contracts
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		24.4	17.8
International | Insurance contracts | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Insurance contracts | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		24.4	17.8
International | Insurance contracts | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Foreign government debt securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		61.0	10.1
International | Foreign government debt securities | Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Foreign government debt securities | Fair Value, Inputs, Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		61.0	10.1
International | Foreign government debt securities | Significant Unobservable Inputs (Level 3)
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0.0	0.0
International | Real estate
Defined Benefit Plan Disclosure [Line Items]
Investments Net Asset Value	[1]	$ 21.2	$ 9.6

[1] Certain investments that are measured at fair value using the net asset value per share practical expedient have not been categorized in the fair value hierarchy. The fair value amounts presented in these tables are intended to permit reconciliation of the fair value hierarchy to the amounts presented in the table that presents our defined benefit pension and post-retirement plans funded status.