Long-Term Debt (3.60% Senior Notes due 2022) (Details) - Senior Notes [Member] - 3.60% Senior Notes Due 2022 [Member] - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Jul. 31, 2012
Debt Instrument [Line Items]
Principal amount	$ 250	$ 250	$ 250
Debt Instrument, Unamortized Discount			$ 1

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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Name:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant