Debt and Credit Agreements Debt Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Sep. 21, 2018
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Redemption Price, Percentage	101.00%
Debt Instrument Change of Control Repurchase Event Price Percentage	101.00%
Term Loan		$ 500.0
3.50% Notes Due 2020
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Issuance Face Amount			$ 500.0
Unamortized Discount at Issuance			1.0
Senior Notes Net of Discount			499.0
Debt Issuance Cost at Issuance			2.9
Senior Notes			496.1
3.75% Notes Due 2021
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			0.3
Senior Notes Net of Discount			499.7
Debt Issuance Cost at Issuance			3.2
Senior Notes			496.5
4.65% Notes Due 2028
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			1.7
Senior Notes Net of Discount			498.3
Debt Issuance Cost at Issuance			4.4
Senior Notes			493.9
5.40% Notes Due 2048
Schedule of New Debt Issuance [Line Items]
Debt Instrument, Face Amount	$ 500.0
Debt Issuance Face Amount			500.0
Unamortized Discount at Issuance			2.8
Senior Notes Net of Discount			497.2
Debt Issuance Cost at Issuance			5.6
Senior Notes			491.6
Aggregate Senior Notes Issued [Domain]
Schedule of New Debt Issuance [Line Items]
Debt Issuance Face Amount			2,000.0
Unamortized Discount at Issuance			5.8
Senior Notes Net of Discount			1,994.2
Debt Issuance Cost at Issuance			16.1
Senior Notes			$ 1,978.1