Long-Term Debt and Commercial Paper (Long-Term Debt) (Details) - USD ($)	9 Months Ended
Sep. 30, 2018	Dec. 31, 2017
Long-term debt	$ 1,980,600,000	$ 2,389,400,000
Less: unamortized debt discounts and debt issuance costs	(13,200,000)	(15,700,000)
Less: current maturities	(5,300,000)	(414,500,000)
Long-term debt, net of current maturities	$ 1,962,100,000	1,959,200,000
6.75% Senior Notes Due 2018 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Apr. 15, 2018
Senior notes	$ 0	400,000,000.0
Percentage interest on debt instrument	6.75%
5.5% Senior Notes Due 2020 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Feb. 01, 2020
Senior notes	$ 350,000,000.0	350,000,000.0
Percentage interest on debt instrument	5.50%
3.35% Senior Notes due 2021 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Jan. 15, 2021
Senior notes	$ 300,000,000.0	300,000,000.0
Percentage interest on debt instrument	3.35%
3.5% Senior Notes Due 2024 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Nov. 15, 2024
Senior notes	$ 450,000,000.0	450,000,000.0
Percentage interest on debt instrument	3.50%
4.5% Senior Notes due 2025 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Oct. 01, 2025
Senior notes	$ 450,000,000.0	450,000,000.0
Percentage interest on debt instrument	4.50%
3.8% Senior Notes Due 2027 [Member] \| Senior Notes [Member]
Debt instrument, maturity date	Nov. 15, 2027
Senior notes	$ 300,000,000.0	300,000,000.0
Percentage interest on debt instrument	3.80%
Revolving Credit Facility Due 2022 [Member]
Revolving credit facility	$ 0	0
Revolving Credit Facility Due 2022 [Member] \| Line of Credit [Member]
Debt instrument, maturity date	Oct. 19, 2022
Capital Leases and Other Debt [Member]
Capital leases and other debt	$ 130,600,000	$ 139,400,000

Amount equal to the present value (the principal) at the beginning of the lease term of minimum lease payments during the lease term (excluding that portion of the payments representing executory costs such as insurance, maintenance, and taxes to be paid by the lessor, together with any profit thereon) net of payments or other amounts applied to the principal through the balance sheet date.

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Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

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