The cumulative amount of the reporting entity's undistributed earnings or deficit.

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

Significant Accounting Policies - Summary of Translation Adjustments in Connection with Adopting CECL (Parenthetical) (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Jan. 02, 2020	Dec. 31, 2019
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reduction in equity (retained earnings), net of tax resulted from current expected credit losses	$ (3,175)		$ (3,664)
ASU 2016-13 [Member] \| Non-PCD Portfolio [Member] \| Cumulative Effect Period of Adoption Adjustment [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Reduction in equity (retained earnings), net of tax resulted from current expected credit losses		$ 620