Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

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Debt (Narrative) (Details) - USD ($)	1 Months Ended	6 Months Ended
Debt (Narrative) (Details) - USD ($)	Apr. 30, 2017	Jun. 30, 2018	Dec. 31, 2017	Jan. 31, 2017
Debt Instrument [Line Items]
Commercial paper outstanding		$ 175,000,000	$ 0
Repayments of senior debt	$ 250,000,000
4.20% Senior Debt Obligations Due 2048
Debt Instrument [Line Items]
Proceeds from issuance of debt		$ 600,000,000
Interest rate		4.20%
2.75% Senior Debt Obligations Due 2022
Debt Instrument [Line Items]
Proceeds from issuance of debt				$ 500,000,000
Interest rate		2.75%		2.75%
4.35% Senior Debt Obligation Due 2047
Debt Instrument [Line Items]
Proceeds from issuance of debt				$ 500,000,000
Interest rate		4.35%		4.35%
3.30% Senior Debt Obligations Due 2023
Debt Instrument [Line Items]
Interest rate		3.30%
Amended Revolving Credit Facility March 27, 2014
Debt Instrument [Line Items]
Debt facilities, maximum borrowing capacity		$ 1,500,000,000
Term of debt		5 years
Revolving credit facility, amount outstanding		$ 0
Commercial Paper
Debt Instrument [Line Items]
Debt financing program		$ 1,500,000,000
Effective interest rate		2.25%