Reclassification Out of Accumulated Other Comprehensive Income (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost		$ 13	$ 8	$ 13
Income Before Income Taxes		2,365	2,028	2,598
Applicable income tax expense		659	545	772
Net income		1,712	1,481	1,836
Total reclassifications for the period
Reclassifications Out Of Accumulated Other Comprehensive Income
Net income		48	45	15
Net unrealized gains on available-for-sale securities
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net losses (gains) included in net income	[1]	16	37	(6)
Income Before Income Taxes	[1]	16	37	(6)
Applicable income tax expense	[1]	(6)	(13)	2
Net income	[1]	10	24	(4)
Net unrealized gains on cash flow hedge derivatives
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income		75	44	44
Income Before Income Taxes	[1]	75	44	44
Applicable income tax expense	[1]	(26)	(15)	(15)
Net income	[1]	49	29	29
Net unrealized gains on cash flow hedge derivatives | Interest rate contracts related to C&I loans
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	[1]	75	44	45
Net unrealized gains on cash flow hedge derivatives | Interest rate contracts related to long-term debt
Reclassifications Out Of Accumulated Other Comprehensive Income
Reclassification adjustment for net gains on cash flow hedge derivatives included in net income	[1]			(1)
Amortization of defined periodic benefit costs
Reclassifications Out Of Accumulated Other Comprehensive Income
Income Before Income Taxes	[1]	(17)	(12)	(16)
Applicable income tax expense	[1]	6	4	6
Net income	[1]	(11)	(8)	(10)
Amortization of defined periodic benefit costs | Amortization of net actuarial (loss) gain
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	(10)	(7)	(11)
Amortization of defined periodic benefit costs | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	$ (7)	$ (5)	$ (5)

[1] Amounts in parentheses indicate reductions to net income.

[2] This AOCI component is included in the computation of net periodic benefit cost. Refer to Note 21 for information on the computation of net periodic benefit cost.