Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	$ 948	$ 567	$ 1,825	$ 1,129
Interest expense — Long-term debt	(74)	(50)	(142)	(96)
Income (loss) from continuing operations before income taxes	579	275	1,009	526
Income taxes	158	69	252	125
INCOME (LOSS) FROM CONTINUING OPERATIONS	407	198	732	385
Personnel expense	551	427	1,107	831
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	4	21	18	43
Income taxes	2	8	7	16
INCOME (LOSS) FROM CONTINUING OPERATIONS	2	13	11	27
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans	5	22
Interest expense — Long-term debt	(1)	(1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes	(4)	(4)	(8)	(8)
Income taxes	(2)	(2)	(3)	(3)
INCOME (LOSS) FROM CONTINUING OPERATIONS	(2)	(2)	(5)	(5)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization of Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	$ (4)	$ (4)	(8)	(8)
Interest Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member] | Interest Rate [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest income — Loans			20	45
Interest Expense [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Interest expense — Long-term debt			$ (2)	$ (2)