Stockholders' Equity - Reclassifications from AOCI (Detail) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-interest income									$ 659	$ 608	$ 305
Non-interest income - OTTI									(30)	(24)	(41)
Interest income	$ 4,961	$ 4,760	$ 4,537	$ 4,576	$ 4,656	$ 4,497	$ 4,315	$ 4,350	18,834	17,818	18,106
Income from continuing operations before income taxes	1,334	1,648	1,236	1,663	1,420	1,661	1,785	1,703	5,881	6,569	6,578
Income tax provision (benefit)	426	530	384	529	450	536	581	579	1,869	2,146	2,224
Net income	$ 920	$ 1,114	$ 863	$ 1,153	$ 999	$ 1,081	$ 1,194	$ 1,154	4,050	4,428	4,121
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net income									62	35	(21)
Accumulated Net Unrealized Investment Gain (Loss) | Reclassification out of Accumulated Other Comprehensive Income [Member] | Securities Available for Sale
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-interest income									(2)	21	7
Non-interest income - OTTI									(30)	(24)	(41)
Income from continuing operations before income taxes									(32)	(3)	(34)
Income tax provision (benefit)									(12)	(1)	(12)
Net income									(20)	(2)	(22)
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									(151)	(131)	(29)
Income tax provision (benefit)									(55)	(55)	(11)
Net income									(96)	(76)	(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									277	173	51
Income tax provision (benefit)									103	65	20
Net income									174	108	31
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									303	209	86
Cash Flow Hedges | Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign exchange contracts
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Non-interest income									(21)	(36)	(35)
Interest income									(5)	0	0
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									5	11	(13)
Income tax provision (benefit)									1	6	(1)
Net income									$ 4	$ 5	$ (12)