Fair Value Measurements - Not Carried at Fair Value (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans		$ 1,858
Commercial mortgage loans, including disposal groups	$ 1,947
Estimate Of Fair Value Fair Value Disclosure [Member] \| Fair Value Inputs Level 2 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Long-term debt, including current maturities, excluding finance leases	39,439	40,819
Estimate Of Fair Value Fair Value Disclosure [Member] \| Fair Value Inputs Level 3 [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans		1,832
Commercial mortgage loans, including disposal groups	1,989
Carrying Reported Amount Fair Value Disclosure [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Commercial mortgage loans		1,858
Commercial mortgage loans, including disposal groups	1,947
Long-term debt, including current maturities, excluding finance leases	$ 36,375	$ 40,829

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio (before reclassification to disposal group assets held for sale).

No definition available.

+ Details

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- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

No definition available.

+ Details

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- Definition

The balance represents the amount of loans that are secured by real estate mortgages, offset by the reserve to cover probable credit losses on the loan portfolio.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(c))
-URI http://asc.fasb.org/extlink&oid=119400593&loc=d3e572229-122910

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