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Long-Term Debt (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Aug. 31, 2020	Aug. 18, 2020	Apr. 13, 2020
Debt Instrument [Line Items]
Debt Instrument Tendered			$ 969.3
Gain (Loss) on Extinguishment of Debt	$ (243.4)	$ 0.0	(243.4)	$ 0.0
Working Capital Adjustment	$ 5.3		$ 5.3
3.60% Notes Due 2030 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.60%		3.60%
0.95% Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						0.95%
1.70% Notes Due 2031 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage						1.70%
4.45% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	4.45%		4.45%		4.45%
2.65% Notes Due 2022 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	2.65%		2.65%		2.65%
3.85% Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.85%		3.85%		3.85%
3.65% Notes Due 2023 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	3.65%		3.65%		3.65%
6.25% Notes Due 2040 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					6.25%
5.95% Notes Due 2041 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					5.95%
Senior Note Redeemed August & September 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount	$ 609.3		$ 609.3
Gain (Loss) on Extinguishment of Debt	$ 231.7
5.89% Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage	5.89%		5.89%
Note Redeemed September 2020 [Member]
Debt Instrument [Line Items]
Debt Instrument, Repurchased Face Amount	$ 25.0		$ 25.0
Gain (Loss) on Extinguishment of Debt	$ 11.7
6.26% Notes Due 2028 [Member]
Debt Instrument [Line Items]
Debt Instrument, Interest Rate, Stated Percentage					6.26%
Senior Notes
Debt Instrument [Line Items]
Debt Instrument, Face Amount							$ 1,000.0
Senior Notes | 3.60% Notes Due 2030 [Member]
Debt Instrument [Line Items]
Proceeds from Debt, Net of Issuance Costs			987.8
Senior Notes | 0.95% Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 1,250.0
Senior Notes | 1.70% Notes Due 2031 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount						$ 750.0
Senior Notes | 0.95% Notes Due 2025 and 1.70% Notes Due 2031 [Member]
Debt Instrument [Line Items]
Proceeds from Debt, Net of Issuance Costs			$ 1,980.4

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