Fair Value Measurements - Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Carrying Value
Financial Instruments
Long-term debt, excluding current portion	$ 16,193	$ 17,989
Fair Value
Financial Instruments
Long-term debt, excluding current portion	$ 17,836	$ 20,496

Fair value portion of debt instrument payable, including, but not limited to, notes payable and loans payable.

Reference 1: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 55
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-URI http://asc.fasb.org/extlink&oid=123466577&loc=SL123495737-112612

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 55
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-Section 50
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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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-Section 50
-Paragraph 1D
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-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495340-112611

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