Stockholders' Equity - Reclassifications from AOCI (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 5,791	$ 5,718
Non-interest income	157	108
Income from continuing operations before income taxes	1,719	1,662
Income tax provision (benefit)	309	319
Net income	1,412	1,346
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	(153)	56
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	24	8
Income tax provision (benefit)	6	2
Net income	18	6
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	(8)	(24)
Income tax provision (benefit)	(2)	(6)
Net income	(6)	(18)
Cash Flow Hedges | 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	(220)	89
Income tax provision (benefit)	(54)	22
Net income	(166)	67
Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Interest rate contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	(60)	6
Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign exchange contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	12	8
Non-interest income	(172)	75
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	1	1
Income tax provision (benefit)	0	0
Net income	$ 1	$ 1