Fair Value Measurements - Financial Assets Liabilities Summary (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
Total assets	$ 1,132,059	$ 1,141,523	$ 992,968
Total level 3 financial assets divided by total assets	2.40%	2.60%	2.30%
Total level 3 financial assets divided by total financial assets at fair value	4.40%	4.60%	4.30%
Total financial liabilities at fair value	$ 373,040	$ 370,824	$ 332,959
Total liabilities	$ 1,039,409	$ 1,051,494	$ 902,703
Total level 3 financial liabilities divided by total liabilities	3.10%	2.90%	2.90%
Total level 3 financial liabilities divided by total financial liabilities at fair value	8.70%	8.10%	7.80%
Counterparty and Cash Collateral Netting [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	$ (74,547)	$ (73,749)	$ (55,527)
Total financial liabilities at fair value	(53,446)	(57,098)	(41,671)
Investments in funds at NAV [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	3,517	3,710	4,206
Level 1 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	281,667	275,444	242,562
Total financial liabilities at fair value	94,637	98,901	54,790
Level 2 [Member]
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total financial assets at fair value	391,698	406,880	325,259
Total financial liabilities at fair value	299,520	298,915	293,902
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
Total financial liabilities at fair value	$ 32,329	$ 30,106	$ 25,938