Fair Value Option - Summary of DVA Losses on Financial Liabilities (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Fair Value, Option, Quantitative Disclosures [Line Items]
DVA (net of tax)	$ (268)	$ 278	$ 428	$ (1,450)
Other Financial Liabilities [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
DVA (pre-tax)	(357)	372	576	(1,930)
DVA (net of tax)	$ (268)	$ 278	$ 428	$ (1,450)