Debt and Credit Facilities (Long-Term Debt Excluding Current Maturities) (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017
Long-term debt excluding current maturities	$ 3,739.8	$ 2,957.0
2.875% Senior notes due 2019 [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.875%	2.875%
Long-term debt excluding current maturities	$ 0.0	$ 349.4
Two Point Six Two Five Percent Senior Notes Due Two Thousand Twenty [Member]
Debt Instrument, Interest Rate, Stated Percentage	2.625%	2.625%
Long-term debt excluding current maturities	$ 299.3	$ 298.9
Two Point Nine Percent Senior Notes Due Two Thousand Twenty One [Member] [Member]
Long-term debt excluding current maturities	$ 298.1	$ 0.0
9.00% Debentures Due 2021 [Member]
Debt Instrument, Interest Rate, Stated Percentage	9.00%	9.00%
Long-term debt excluding current maturities	$ 124.9	$ 124.9
4.25% Senior notes due 2023 [Member]
Debt Instrument, Interest Rate, Stated Percentage	4.25%	4.25%
Long-term debt excluding current maturities	$ 697.0	$ 696.5
Seven Point Two Zero Percent Debentures [Domain]
Long-term debt excluding current maturities	$ 44.8	$ 52.3
Three Point Five Five Percent Senior Notes due 2024 [Member]
Debt Instrument, Interest Rate, Stated Percentage	3.55%	3.55%
Long-term debt excluding current maturities	$ 495.7	$ 495.2
6.48% Debentures Due 2025 [Member]
Debt Instrument, Interest Rate, Stated Percentage	6.48%	6.48%
Long-term debt excluding current maturities	$ 149.7	$ 149.7
Three Point Seven Five Percent Senior Notes Due Two Thousand Twenty Eight [Member]
Long-term debt excluding current maturities	$ 544.3	$ 0.0
5.75% Senior notes due 2043 [Member]
Debt Instrument, Interest Rate, Stated Percentage	5.75%	5.75%
Long-term debt excluding current maturities	$ 494.2	$ 494.0
Four Point Six Five Percent Senior Notes due Twenty Forty Four [Member]
Debt Instrument, Interest Rate, Stated Percentage	4.65%	4.65%
Long-term debt excluding current maturities	$ 295.7	$ 295.6
Other Loans and Notes [Member]
Long-term debt excluding current maturities	$ 0.3	$ 0.5
Seven Point Two Zero Percent Debentures due Two Thousand Fourteen to Two Thousand Twenty Five [Member] [Member]
Debt Instrument, Interest Rate, Stated Percentage	7.20%	7.20%
Four Point Three Percent Senior Notes Due Two Thousand Forty Eight [Member]
Long-term debt excluding current maturities	$ 295.8	$ 0.0