Fair Value of Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019
Financial Liabilities, Balance Sheet Groupings [Abstract]
Long-term Debt, Gross	$ 2,764	$ 2,420
Long-term debt, Fair Value	$ 3,381	$ 2,706

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:	us-gaap_DebtInstrumentCarryingAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant