Stockholders' Equity - Reclassifications from AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 5,555	$ 5,737	$ 17,040	$ 17,274
Interest expense	660	1,338	2,602	3,969
Non-interest income	706	144	1,017	492
Income from continuing operations before income taxes	3,502	1,704	139	5,426
Income tax provision (benefit)	1,096	375	(10)	1,071
Net income	2,406	1,333	148	4,370
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	101	26	305	(252)
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income [Member] | Available-for-sale securities
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-interest income	25	5	25	44
Income tax provision (benefit)	6	2	6	11
Net income	19	3	19	33
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income [Member] | Securities Held to Maturity
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	0	(10)	0	(26)
Income tax provision (benefit)	0	(2)	0	(6)
Net income	0	(8)	0	(20)
Hedging Relationships | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest rate contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	179	(44)	347	(166)
Hedging Relationships | Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign exchange contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	1	12	10	37
Interest expense	(1)	(1)	(3)	(1)
Non-interest income	(73)	71	20	(224)
Income from continuing operations before income taxes	106	38	374	(354)
Income tax provision (benefit)	26	9	90	(86)
Net income	80	29	284	(268)
Other | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from continuing operations before income taxes	2	3	2	4
Income tax provision (benefit)	0	1	0	1
Net income	$ 2	$ 2	$ 2	$ 3