Derivative Financial Instruments Location and Fair Values of Derivative Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Derivative
Asset Derivatives Fair Value	$ 34.9	$ 30.9
Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	34.5	30.4
Designated as Hedging Instrument | Other Long-term Investments | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	21.7
Designated as Hedging Instrument | Other Long-term Investments | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	12.8	5.4
Designated as Hedging Instrument | Other Long-term Investments | Forwards | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	0.0
Designated as Hedging Instrument | Other Long-term Investments | Interest Rate Swaps | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	0.0	0.0
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Asset Derivatives Fair Value	21.7	25.0
Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Asset Derivatives Fair Value	12.8	5.4
Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	11.0	13.5
Designated as Hedging Instrument | Other Liabilities | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	6.7
Designated as Hedging Instrument | Other Liabilities | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	4.3	5.6
Designated as Hedging Instrument | Other Liabilities | Forwards | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	0.1
Designated as Hedging Instrument | Other Liabilities | Interest Rate Swaps | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	1.0	5.2
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Cash Flow Hedging
Derivative
Liability Derivatives Fair Value	6.6	7.9
Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts | Fair Value Hedging
Derivative
Liability Derivatives Fair Value	3.3	0.4
Not Designated as Hedging Instrument | Other Long-term Investments
Derivative
Asset Derivatives Fair Value	0.4	0.5
Not Designated as Hedging Instrument | Other Long-term Investments | Credit Default Swaps
Derivative
Asset Derivatives Fair Value	0.2	0.5
Not Designated as Hedging Instrument | Other Long-term Investments | Foreign Exchange Contracts
Derivative
Asset Derivatives Fair Value	0.2	0.0
Not Designated as Hedging Instrument | Other Long-term Investments | Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Asset Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument | Other Liabilities
Derivative
Liability Derivatives Fair Value	60.4	55.6
Not Designated as Hedging Instrument | Other Liabilities | Credit Default Swaps
Derivative
Liability Derivatives Fair Value	0.0	0.0
Not Designated as Hedging Instrument | Other Liabilities | Foreign Exchange Contracts
Derivative
Liability Derivatives Fair Value	22.9	24.5
Not Designated as Hedging Instrument | Other Liabilities | Embedded Derivative in Modified Coinsurance Arrangement
Derivative
Liability Derivatives Fair Value	$ 37.5	$ 31.1