Long-Term Debt (4.375% Senior Notes due 2047) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Nov. 30, 2017
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 2,715	$ 3,853
Senior Notes [Member] \| 4.375% Senior Notes Due 2047 [Member]
Debt Instrument [Line Items]
Long-term Debt, Gross	$ 500	$ 500	$ 500

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
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-Name Accounting Standards Codification
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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant