AOCI (Reclassification Out of Accumulated Other Comprehensive Income) (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost		$ 16	$ 13	$ 8
Income Before Income Taxes		2,065	2,365	2,028
Applicable income tax expense		505	659	545
Net income		1,564	1,712	1,481
Total reclassifications for the period
Reclassifications Out Of Accumulated Other Comprehensive Income
Net income		26	48	45
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]	11	16	37
Income Before Income Taxes	[1]	11	16	37
Applicable income tax expense	[1]	(4)	(6)	(13)
Net income	[1]	7	10	24
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		48	75	44
Income Before Income Taxes	[1]	48	75	44
Applicable income tax expense	[1]	(17)	(26)	(15)
Net income	[1]	31	49	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]	48	75	44
Amortization of defined periodic benefit costs
Reclassifications Out Of Accumulated Other Comprehensive Income
Income Before Income Taxes	[1]	(18)	(17)	(12)
Applicable income tax expense	[1]	6	6	4
Net income	[1]	(12)	(11)	(8)
Amortization of defined periodic benefit costs | Net Actuarial Loss
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	(11)	(10)	(7)
Amortization of defined periodic benefit costs | Pension Settlement
Reclassifications Out Of Accumulated Other Comprehensive Income
Net periodic pension cost	[1],[2]	$ (7)	$ (7)	$ (5)

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

[2] This AOCI component is included in the computation of net periodi c benefit cost. Refer to Note 20 f or information on the computation of net periodic benefit cost.