Fair Value Measurements - Notional Amounts of Outstanding Derivative Instruments (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Interest rate swaps
Derivative [Line Items]
Notional amount	$ 18,156	$ 17,004
Cross currency swaps
Derivative [Line Items]
Notional amount	24,740	23,070
Forward starting interest rate swaps
Derivative [Line Items]
Notional amount	2,000	3,000
Interest rate caps
Derivative [Line Items]
Notional amount	0	679
Foreign exchange forwards
Derivative [Line Items]
Notional amount	$ 1,300	$ 1,130

Nominal or face amount used to calculate payment on derivative.

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=121590274&loc=SL5579245-113959

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