Debt (Consolidated Debt) (Details) - USD ($)	Jun. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 4,670,000,000	$ 4,550,000,000
Unamortized debt issuance costs	(28,327,000)	(29,472,000)
Net unamortized premium (discount)	(1,418,000)	215,000
Net unamortized amount of gains from historical fair value hedges	1,818,000	3,749,000
Long-term Debt	4,642,073,000	4,524,492,000
Current portion of long-term debt, net	250,046,000	250,974,000
Long-term debt, net	4,392,027,000	4,273,518,000
6.40% Notes Due 2018 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.40%
6.55% Notes Due 2019 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550,000,000	550,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.55%
4.25% Notes Due 2021 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550,000,000	550,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.25%
3.20% Notes Due 2025 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.20%
5.00% Notes Due 2026 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 650,000,000	650,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.00%
6.40% Notes Due 2037 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage	6.40%
4.20% Notes Due 2042 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.20%
5.15% Notes Due 2043 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 550,000,000	550,000,000
Debt Instrument, Interest Rate, Stated Percentage	5.15%
4.20% Notes Due 2045 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 250,000,000	250,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.20%
4.25% Notes Due 2046 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000	500,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.25%
4.20% Notes Due 2047 [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 500,000,000	500,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.20%
Commercial Paper [Member]
Debt Instrument [Line Items]
Debt Instrument, Face Amount	$ 120,000,000	$ 0

Face (par) amount of debt instrument at time of issuance.

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Contractual interest rate for funds borrowed, under the debt agreement.

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Amount, after accumulated amortization, of debt discount (premium).

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount as of the balance sheet date of the unamortized adjustment to the carrying value of an interest-bearing hedged item made under an effective interest rate fair value hedge that is amortized upon discontinuation of the interest rate fair value hedge.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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