Stockholders' Equity - Reclassifications from AOCI (Detail) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income	$ 22,460	$ 20,873	$ 18,834
Non-interest income	542	541	491
Income from continuing operations before income taxes	5,492	5,484	5,881
Income tax provision (benefit)	3,375	1,714	1,869
Net income	1,982	3,751	4,050
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income	58	86	62
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	65	(10)	(32)
Income tax provision (benefit)	24	(4)	(12)
Net income	41	(6)	(20)
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	(150)	(164)	(151)
Income tax provision (benefit)	(53)	(60)	(55)
Net income	(97)	(104)	(96)
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	173	310	277
Income tax provision (benefit)	65	115	103
Net income	108	195	174
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	145	306	303
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	27	6	(5)
Non-interest income	1	(2)	(21)
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	9	2	5
Income tax provision (benefit)	3	1	1
Net income	$ 6	$ 1	$ 4