Financing (Senior Notes) (Narrative) (Details) $ in Millions		12 Months Ended
Aug. 17, 2017 USD ($) d Rate	Dec. 31, 2017 USD ($) d Rate
Financing
Unsecured senior notes description		The Company has issued a cumulative $2.7 billion aggregate principal amount of unsecured senior notes, which are due between 2021 and 2027, with UMB as trustee. Interest on the senior notes, ranging from 3.550% to 4.875%, is payable semi-annually and is computed on the basis of a 360-day year.
Debt instrument covenant description		Each of the senior notes is subject to certain customary covenants, with which the Company complied as of December 31, 2017.
Senior notes [Member]
Financing
Number of days in annual interest calculation period \| d		360
Aggregate principle of unsecured senior notes \| $		$ 2,700
Minimum [Member] \| Senior notes [Member]
Financing
Interest rate of senior notes		3.55%
Senior notes maturity, year		2021
Maximum [Member] \| Senior notes [Member]
Financing
Interest rate of senior notes		4.875%
Senior notes maturity, year		2027
$750 million, 3.600% Senior Notes due 2027 [Member]
Financing
Interest rate of senior notes		3.60%
Senior notes maturity, year		2027
$750 million, 3.600% Senior Notes due 2027 [Member] \| Senior notes [Member]
Financing
Issuance date of senior notes	Aug. 17, 2017
Face amount of senior notes \| $	$ 750	$ 750
Interest rate of senior notes	3.60%
Senior notes maturity, year	2027
Percentage of face value of debt instrument	99.84%
Number of days in annual interest calculation period \| d	360

The year when the debt instrument is scheduled to be fully repaid.

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The percent of face value, at which the debt instrument was offered to the public.

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States whether the entity was in compliance with the debt covenants throughout the reporting period, and describes facts and circumstances of any compliance failure.

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Identification of the lender and information about a contractual promise to repay a short-term or long-term obligation, which includes borrowings under lines of credit, notes payable, commercial paper, bonds payable, debentures, and other contractual obligations for payment. This may include rationale for entering into the arrangement, significant terms of the arrangement, which may include amount, repayment terms, priority, collateral required, debt covenants, borrowing capacity, call features, participation rights, conversion provisions, sinking-fund requirements, voting rights, basis for conversion if convertible and remarketing provisions. The description may be provided for individual debt instruments, rational groupings of debt instruments, or by debt in total.

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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 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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