Fair Value Measurements - Total Level 3 Financial Assets (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	$ 539,568	$ 501,712
Investment at fair value	57,827	45,579
Loans receivable at fair value	14,386	13,416
Financial assets fair value disclosure	112,023	162,522
Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	100,779	94,229
Level 3 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	23,068	22,181
Loans receivable at fair value	1,890	1,990
Financial assets fair value disclosure		6
Level 3 [Member] | Trading cash instruments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Trading cash instrument at fair value	1,242	1,689
Level 3 [Member] | Derivatives [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	4,654	4,948
Level 3 [Member] | Investments [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Investment at fair value	15,282	13,548
Level 3 [Member] | Loans [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Loans receivable at fair value	$ 1,890	1,990
Level 3 [Member] | Other Assets at Fair Value [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Financial assets fair value disclosure		$ 6