Accumulated Other Comprehensive Income - Reclassifications Out of AOCI (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Corporate services income	$ 57	$ 42	$ 143	$ 125
Income taxes	72	64	230	232
Income (loss) from continuing operations	220	203	686	694
Personnel expense	(426)	(405)	(1,223)	(1,182)
Interest income - Loans	542	531	1,597	1,576
Interest expense - Long term debt	(41)	(33)	(118)	(98)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income (loss) from continuing operations before income taxes			(1)
Income (loss) from continuing operations			(1)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Securities Available for Sale [Member] | Realized Losses [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income			(1)
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	27	18	70	46
Income taxes	10	7	26	17
Income (loss) from continuing operations	17	11	44	29
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	28	18	73	49
Interest expense - Long term debt	(1)	(1)	(3)	(3)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized Gains (Losses) on Derivative Financial Instruments [Member] | Foreign Exchange [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Other income		1
Reclassification out of Accumulated Other Comprehensive Income [Member] | Foreign Currency Translation Adjustment [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Corporate services income	(1)		(2)	3
Income (loss) from continuing operations before income taxes	(1)		(2)	3
Income taxes	1		1
Income (loss) from continuing operations			(1)	3
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	(23)	(24)	(31)	32
Income taxes	(9)	(10)	12	(13)
Income (loss) from continuing operations	(14)	(14)	(19)	(19)
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)	(13)	(12)
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Amortization Of Unrecognized Prior Service Cost [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense	$ (19)		1
Reclassification out of Accumulated Other Comprehensive Income [Member] | Net Pension and Postretirement Benefit Costs [Member] | Settlement Loss [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Personnel expense		$ (20)	$ (19)	$ (20)