Fair Value Measurements - Total Level 3 Financial Assets (Detail) - USD ($) $ in Millions	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	$ 630,012	$ 641,711	$ 539,568
Investment at fair value	74,714		57,827
Loans receivable at fair value	13,881		14,386
Financial assets fair value disclosure	133,017		112,023
Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	139,067		100,779
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	27,677	29,426	23,068
Loans receivable at fair value	2,827		1,890
Financial assets fair value disclosure	27,677	29,426	23,068
Level 3 [Member] | Trading cash instruments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading cash instrument at fair value	1,265	1,804	1,242
Level 3 [Member] | Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	6,311	7,047	4,654
Level 3 [Member] | Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment at fair value	17,274	17,916	15,282
Level 3 [Member] | Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans receivable at fair value	$ 2,827	$ 2,659	$ 1,890