Stockholders' Equity - Reclassifications from AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 5,460	$ 5,746	$ 11,485	$ 11,537
Interest expense	858	1,330	1,942	2,631
Non-interest income	166	191	311	348
Income (loss) from continuing operations before income taxes	(1,460)	2,003	(3,363)	3,722
Income tax provision (benefit)	(543)	387	(1,106)	696
Net income (loss)	(918)	1,625	(2,258)	3,037
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income (loss)	(117)	(125)	204	(278)
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	0	15	0	39
Income tax provision (benefit)	0	3	0	9
Net income (loss)	0	12	0	30
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	(8)	0	(16)
Income tax provision (benefit)	0	(2)	0	(4)
Net income (loss)	0	(6)	0	(12)
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	142	(62)	168	(122)
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	2	13	9	25
Interest expense	(1)	0	(2)	0
Non-interest income	(299)	(123)	93	(295)
Income (loss) from continuing operations before income taxes	(156)	(172)	268	(392)
Income tax provision (benefit)	(39)	(41)	64	(95)
Net income (loss)	(117)	(131)	204	(297)
Other | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	0	0	0	1
Income tax provision (benefit)	0	0	0	0
Net income (loss)	$ 0	$ 0	$ 0	$ 1